Motion vector prediction in video coding

ABSTRACT

Aspects of this disclosure relate to a method of coding video data. In an example, the method includes identifying a first block of video data in a first temporal location from a first view, wherein the first block of video data is associated with a first temporal motion vector. The method also includes determining, when a second motion vector associated with a second block of video data comprises a temporal motion vector and the second block is from a second view, a motion vector predictor for the second motion vector based on the first temporal motion vector. The method also includes coding prediction data for the second block using the motion vector predictor.

This disclosure claims priority to U.S. Provisional Application No.61/477,561, filed Apr. 20, 2011 and U.S. Provisional Application No.61/512,765, filed Jul. 28, 2011, the contents of both of which areincorporated by reference in their entirety.

TECHNICAL FIELD

This disclosure relates to video coding.

BACKGROUND

Digital video capabilities can be incorporated into a wide range ofdevices, including digital televisions, digital direct broadcastsystems, wireless broadcast systems, personal digital assistants (PDAs),laptop or desktop computers, tablet computers, e-book readers, digitalcameras, digital recording devices, digital media players, video gamingdevices, video game consoles, cellular or satellite radio telephones,so-called “smart phones,” video teleconferencing devices, videostreaming devices, and the like. Digital video devices implement videocompression techniques, such as those described in the standards definedby MPEG-2, MPEG-4, ITU-T H.263, ITU-T H.264/MPEG-4, Part 10, AdvancedVideo Coding (AVC), the High Efficiency Video Coding (HEVC) standardpresently under development, and extensions of such standards. The videodevices may transmit, receive, encode, decode, and/or store digitalvideo information more efficiently by implementing such videocompression techniques.

Video compression techniques perform spatial (intra-picture) predictionand/or temporal (inter-picture) prediction to reduce or removeredundancy inherent in video sequences. For block-based video coding, avideo slice (i.e., a picture or a portion of a picture) may bepartitioned into video blocks, which may also be referred to astreeblocks, coding units (CUs) and/or coding nodes. Video blocks in anintra-coded (I) slice of a picture are encoded using spatial predictionwith respect to reference samples in neighboring blocks in the samepicture. Video blocks in an inter-coded (P or B) slice of a picture mayuse spatial prediction with respect to reference samples in neighboringblocks in the same picture or temporal prediction with respect toreference samples in other reference pictures.

Spatial or temporal prediction results in a predictive block for a blockto be coded. Residual data represents pixel differences between theoriginal block to be coded and the predictive block. An inter-codedblock is encoded according to a motion vector that points to a block ofreference samples forming the predictive block, and the residual dataindicating the difference between the coded block and the predictiveblock. An intra-coded block is encoded according to an intra-coding modeand the residual data. For further compression, the residual data may betransformed from the pixel domain to a transform domain, resulting inresidual transform coefficients, which then may be quantized. Thequantized transform coefficients, initially arranged in atwo-dimensional array, may be scanned in order to produce aone-dimensional vector of transform coefficients, and entropy coding maybe applied to achieve even more compression.

SUMMARY

In general, this disclosure describes techniques for coding video data.This disclosure describes techniques for performing motion vectorprediction, motion estimation and motion compensation when inter-modecoding (i.e., coding a current block relative to blocks of otherpictures) in Multiview Video Coding (MVC). In general, MVC is a videocoding standard for encapsulating multiple views of video data. Eachview may correspond to a different perspective, or angle, at whichcorresponding video data of a common scene was captured. The techniquesof this disclosure generally include predicting motion prediction datain the context of multiview video coding. That is, for example,according to the techniques of this disclosure a disparity motion vectorfrom a block in the same or a different view than a block currentlybeing coded may be used to predict the motion vector of the currentblock. In another example, according to the techniques of thisdisclosure a temporal motion vector from a block in the same or adifferent view that a block currently being coded may be used to predictthe motion vector of the current block.

In an example, aspects of this disclosure relate to a method of codingvideo data, the method comprising identifying a first block of videodata in a first temporal location from a first view, wherein the firstblock is associated with a first disparity motion vector; determining amotion vector predictor for a second motion vector associated with asecond block of video data, wherein the motion vector predictor is basedon the first disparity motion vector; wherein, when the second motionvector comprises a disparity motion vector, determining the motionvector predictor comprises scaling the first disparity motion vector togenerate a scaled motion vector predictor, wherein scaling the firstdisparity motion vector comprises applying a scaling factor comprising aview distance of the second disparity motion vector divided by a viewdistance of the first motion vector to the first disparity motionvector; and coding prediction data for the second block using the scaledmotion vector predictor.

In another example, aspects of this disclosure relate to an apparatusfor coding video data comprising one or more processors, the one or moreprocessors configured to identify a first block of video data in a firsttemporal location from a first view, wherein the first block isassociated with a first disparity motion vector; determine a motionvector predictor for a second motion vector associated with a secondblock of video data, wherein the motion vector predictor is based on thefirst disparity motion vector; wherein, when the second motion vectorcomprises a disparity motion vector, the one or more processors areconfigured to determine the motion vector predictor by scaling the firstdisparity motion vector to generate a scaled motion vector predictor,wherein scaling the first disparity motion vector comprises applying ascaling factor comprising a view distance of the second disparity motionvector divided by a view distance of the first motion vector to thefirst disparity motion vector; and code prediction data for the secondblock based on the scaled motion vector predictor.

In another example, aspects of this disclosure relate to an apparatusfor coding video data comprising means for identifying a first block ofvideo data in a first temporal location from a first view, wherein thefirst block is associated with a first disparity motion vector; meansfor determining a motion vector predictor for a second motion vectorassociated with a second block of video data, wherein the motion vectorpredictor is based on the first disparity motion vector; wherein, whenthe second motion vector comprises a disparity motion vector, the meansfor determining the motion vector predictor are configured to determinethe motion vector predictor by scaling the first disparity motion vectorto generate a scaled motion vector predictor, wherein scaling the firstdisparity motion vector comprises applying a scaling factor comprising aview distance of the second disparity motion vector divided by a viewdistance of the first motion vector to the first disparity motionvector; and means for coding prediction data for the second block basedon the scaled motion vector predictor.

In another example, aspects of this disclosure relate to acomputer-readable storage medium having stored thereon instructionsthat, upon execution, cause one or more processors to identify a firstblock of video data in a first temporal location from a first view,wherein the first block is associated with a first disparity motionvector; determine a motion vector predictor for a second motion vectorassociated with a second block of video data, wherein the motion vectorpredictor is based on the first disparity motion vector; wherein, whenthe second motion vector comprises a disparity motion vector, theinstructions cause the one or more processors to determine the motionvector predictor by scaling the first disparity motion vector togenerate a scaled motion vector predictor, wherein scaling the firstdisparity motion vector comprises applying a scaling factor comprising aview distance of the second disparity motion vector divided by a viewdistance of the first motion vector to the first disparity motionvector; and code prediction data for the second block based on thescaled motion vector predictor.

In another example, aspects of this disclosure relate to a method ofcoding video data, the method comprising identifying a first block ofvideo data in a first temporal location from a first view, wherein thefirst block of video data is associated with a first temporal motionvector; determining, when a second motion vector associated with asecond block of video data comprises a temporal motion vector and thesecond block is from a second view, a motion vector predictor for thesecond motion vector based on the first temporal motion vector; andcoding prediction data for the second block using the motion vectorpredictor.

In another example, aspects of this disclosure relate to an apparatusfor coding video data comprising one or more processors configured toidentify a first block of video data in a first temporal location from afirst view, wherein the first block of video data is associated with afirst temporal motion vector; determine, when a second motion vectorassociated with a second block of video data comprises a temporal motionvector and the second block is from a second view, a motion vectorpredictor for the second motion vector based on the first temporalmotion vector; and code prediction data for the second block using themotion vector predictor.

In another example, aspects of this disclosure relate to an apparatusfor coding video data comprising means for identifying a first block ofvideo data in a first temporal location from a first view, wherein thefirst block of video data is associated with a first temporal motionvector; means for determining, when a second motion vector associatedwith a second block of video data comprises a temporal motion vector andthe second block is from a second view, a motion vector predictor forthe second motion vector based on the first temporal motion vector; andmeans for coding prediction data for the second block using the motionvector predictor.

In an example, aspects of this disclosure relate to a computer-readablestorage medium having stored thereon instructions that, upon execution,cause one or more processors to identify a first block of video data ina first temporal location from a first view, wherein the first block ofvideo data is associated with a first temporal motion vector; determine,when a second motion vector associated with a second block of video datacomprises a temporal motion vector and the second block is from a secondview, a motion vector predictor for the second motion vector based onthe first temporal motion vector; and code prediction data for thesecond block using the motion vector predictor.

The details of one or more aspects of the disclosure are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the techniques described in this disclosurewill be apparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating an example video encoding anddecoding system that may utilize the techniques described in thisdisclosure.

FIG. 2 is a block diagram illustrating an example video encoder that mayimplement the techniques described in this disclosure.

FIG. 3 is a block diagram illustrating an example video decoder that mayimplement the techniques described in this disclosure.

FIG. 4 is a is a conceptual diagram illustrating an example MultiviewVideo Coding (MVC) prediction pattern.

FIG. 5 is a block diagram illustrating example locations for motionvector predictor candidates.

FIG. 6 is a conceptual diagram illustrating generating and scaling amotion vector predictor, according to aspects of this disclosure.

FIG. 7 is another conceptual diagram illustrating generating and scalinga motion vector predictor, according to aspects of this disclosure.

FIG. 8 is another conceptual diagram illustrating generating and scalinga motion vector predictor, according to aspects of this disclosure.

FIG. 9 is a flow diagram illustrating an example method of codingprediction information for a block of video data.

FIG. 10 is a conceptual diagram illustrating generating a motion vectorpredictor from a block in a different view than a current block.

FIG. 11 is a flow diagram illustrating an example method of generating amotion vector predictor from a block in a different view than a currentblock.

DETAILED DESCRIPTION

According to certain video coding systems, motion estimation and motioncompensation may be used to reduce the temporal redundancy in a videosequence, so as to achieve data compression. In this case, a motionvector can be generated that identifies a predictive block of videodata, e.g., a block from another video picture or slice, which can beused to predict the values of the current video block being coded. Thevalues of the predictive video block are subtracted from the values ofthe current video block to produce a block of residual data. Motioninformation (e.g., a motion vector, motion vector indexes, predictiondirections, or other information) is communicated from a video encoderto a video decoder, along with the residual data. The decoder can locatethe same predictive block (based on the motion vector) and reconstructthe encoded video block by combining the residual data with the data ofthe predictive block.

In some cases, predictive coding of motion vectors is also applied tofurther reduce the amount of data needed to communicate the motionvector. When a motion vector is established, it is from a target pictureto a reference picture. A motion vector can be spatially or temporallypredicted. A spatially predicted motion vector is associated withavailable spatial blocks (a block of the same time instance). Atemporally predicted motion vector is associated with available temporalblocks (a block of a different time instance). In the case of motionvector prediction, rather than encoding and communicating the motionvector itself, the encoder encodes and communicates a motion vectordifference (MVD) relative to a known (or knowable) motion vector. InH.264/AVC, the known motion vector, which may be used with the MVD todefine the current motion vector, can be defined by a so-called motionvector predictor (MVP). To be a valid MVP, the motion vector must pointto the same picture as the motion vector currently being coded by theMVP and the MVD.

A video coder may build a motion vector predictor candidate list thatincludes several neighboring blocks in spatial and temporal directionsas candidates for MVP. In this case, a video encoder may select the mostaccurate predictor from the candidate set based on analysis of encodingrate and distortion (e.g., using a rate-distortion cost analysis orother coding efficiency analysis). A motion vector predictor index(mvp_idx) can be transmitted to a video decoder to inform the decoderwhere to locate the MVP. The MVD is also communicated. The decoder cancombine the MVD with the MVP (defined by the motion vector predictorindex) so as to reconstruct the motion vector.

A so-called “merge mode” may also be available, in which motioninformation (such as motion vectors, reference picture indexes,prediction directions, or other information) of a neighboring videoblock are inherited for a current video block being coded. An indexvalue may be used to identify the neighbor from which the current videoblock inherits its motion information.

Multiview Video Coding (MVC) is a video coding standard forencapsulating multiple views of video data. In general, each viewcorresponds to a different perspective, or angle, at which correspondingvideo data of a common scene was captured. MVC provides a set ofmetadata, that is, descriptive data for the views collectively andindividually.

The coded views can be used for three-dimensional (3D) display of videodata. For example, two views (e.g., left and right eye views of a humanviewer) may be displayed simultaneously or near simultaneously usingdifferent polarizations of light, and a viewer may wear passive,polarized glasses such that each of the viewer's eyes receives arespective one of the views. Alternatively, the viewer may wear activeglasses that shutter each eye independently, and a display may rapidlyalternate between images of each eye in synchronization with theglasses.

In MVC, a particular picture of a particular view is referred to as aview component. That is, a view component of a view corresponds toparticular temporal instance of the view. Typically, the same orcorresponding objects of two views are not co-located. The term“disparity vector” may be used to refer to a vector that indicatesdisplacement of an object in a picture of a view relative to thecorresponding object in a different view. Such a vector may also bereferred to as a “displacement vector.” A disparity vector may also beapplicable to a pixel or a block of video data of a picture. Forexample, a pixel in a picture of a first view may be displaced withrespect to a corresponding pixel in a picture of a second view by aparticular disparity related to differing camera locations from whichthe first view and second view are captured. In some examples, disparitycan be used to predict a motion vector from one view to another view.

In the context of MVC, pictures of one view may be predicted frompictures of another view. For example, a block of video data may bepredicted relative to a block of video data in a reference picture ofthe same temporal instance, but of a different view. In an example, ablock that is currently being coded may be referred to as a “currentblock.” A motion vector predicting the current block from a block in adifferent view but in the same time instance is called “disparity motionvector.” A disparity motion vector is typically applicable in thecontext of multiview video coding, where more than one view may beavailable. According to this disclosure, a “view distance” for adisparity motion vector may refer to a translation difference betweenthe view of the reference picture and the view of the target picture.That is, a view distance may be represented as a view identifierdifference between a view identifier of the reference picture and a viewidentifier of the target picture.

Another type of motion vector is a “temporal motion vector.” In thecontext of multiview video coding, a temporal motion vector refers to amotion vector predicting a current block from a block in a differenttime instance, but within the same view. According to this disclosure, a“temporal distance” of a temporal motion vector may refer to a pictureorder count (POC) distance from the reference picture to the targetpicture.

Certain techniques of this disclosure are directed to using motioninformation (e.g., a motion vector, motion vector indexes, predictiondirections, or other information) associated with a block of video datain a multiview setting to predict a motion information of a blockcurrently being coded. For example, according to aspects of thisdisclosure, a motion vector predicted from a different view can be addedas a candidate for one or more motion vector lists used for motionvector prediction of the current block. In some examples, a video codermay use a disparity motion vector associated with a block in a differentview than a block currently being coded to predict a motion vector forthe current block, and may add the predicted disparity motion vector toa candidate motion vector list. In other examples, a video coder may usea temporal motion vector associated with a block in a different viewthan a block currently being coded to predict a motion vector for thecurrent block, and may add the predicted temporal motion vector to acandidate motion vector list.

According to aspects of this disclosure, a disparity motion vector maybe scaled before being used as a motion vector predictor for a blockcurrently being coded. For example, if a disparity motion vectoridentifies a reference picture that has the same view identifier as acurrent motion vector being predicted, and the disparity motion vectorhas a target picture with the same view identifier as the current motionvector being predicted, the disparity motion vector may not be scaledbefore being used to predict the motion vector for the current block. Inother instances, the disparity motion vector may be scaled before beingused to predict the motion vector for the current block.

In another example, a disparity motion vector may be predicted from adisparity motion vector associated with a spatially neighboring block.In this example, if the view identifier of the reference picture of thedisparity motion vector is the same as that of the reference picture ofthe motion vector to be predicted (e.g., the motion vector associatedwith the block currently being predicted), no scaling may be needed.Otherwise, the disparity motion vector may be scaled based on a cameralocation of a camera used to capture the video data. That is, forexample, the disparity motion vector being used for prediction may bescaled according to a difference between the view identifier of thereference picture of the disparity motion vector and the view identifierof the target picture of the motion vector. In some examples, thedisparity motion vector scaling may be scaled based on the translationsof the views.

In another example, a disparity motion vector may be predicted from adisparity motion vector associated with a temporally neighboring block.In this example, if the view identifier of the reference picture of thedisparity motion vector is the same as that of the reference picture ofthe motion vector to be predicted, and the view identifier of the targetpicture of the disparity motion vector is the same as that of thereference picture of the motion vector to be predicted, no scaling maybe needed. Otherwise, the disparity motion vector may be scaled based ona difference in view identifier, as described with respect to theprevious example.

Regarding temporal motion vector prediction, according to aspects ofthis disclosure, a temporal motion vector that has a target picture in afirst view may be used to predict a temporal motion vector that has atarget picture in a second, different view. In some examples, the blockin the target picture of the temporal motion vector being used forprediction may be co-located with the block currently being predicted ina different view. In other examples, the block in the target picture ofthe temporal motion vector being used for prediction may be offset fromthe current block, due to a disparity between the two views.

In some examples, when a motion vector being predicted from a differentview is a temporal motion vector, the motion vector might be scaledbased on a difference in picture order count (POC) distances. Forexample, according to aspects of this disclosure, if a reference pictureof the temporal motion vector being used for prediction has the same POCvalue as the reference picture of the current motion vector beingpredicted, and the target picture of the temporal motion vector beingused for prediction has the same POC value as the reference picture ofthe current motion vector being predicted, the motion vector being usedfor prediction may not be scaled. Otherwise, however, the motion vectorbeing used for prediction may be scaled based on a difference in POCvalue between the reference picture of the motion vector being used forprediction and the reference picture of the motion vector currentlybeing predicted.

According to some aspects of this disclosure, temporal and/or disparitymotion vectors from different views may be used as MVP candidates. Forexample, the temporal and/or disparity motion vectors may be used tocalculate an MVD for a current block. According to other aspects of thisdisclosure, temporal and/or disparity motion vectors from differentviews may be used as merge candidates. For example, the temporal and/ordisparity motion vectors may be inherited for a current block. In suchexamples, an index value may be used to identify the neighbor from whichthe current video block inherits its motion information. In any event, adisparity and/or temporal motion vector from a different view being usedas an MVP or merge candidate may be scaled before being used as the MVPor merge candidate.

FIG. 1 is a block diagram illustrating an example video encoding anddecoding system 10 that may utilize techniques for motion vectorprediction in multiview coding. As shown in FIG. 1, system 10 includes asource device 12 that provides encoded video data to be decoded at alater time by a destination device 14. In particular, source device 12provides the video data to destination device 14 via a computer-readablemedium 16. Source device 12 and destination device 14 may comprise anyof a wide range of devices, including desktop computers, notebook (i.e.,laptop) computers, tablet computers, set-top boxes, telephone handsetssuch as so-called “smart” phones, so-called “smart” pads, televisions,cameras, display devices, digital media players, video gaming consoles,video streaming device, or the like. In some cases, source device 12 anddestination device 14 may be equipped for wireless communication.

Destination device 14 may receive the encoded video data to be decodedvia computer-readable medium 16. Computer-readable medium 16 maycomprise any type of medium or device capable of moving the encodedvideo data from source device 12 to destination device 14. In oneexample, computer-readable medium 16 may comprise a communication mediumto enable source device 12 to transmit encoded video data directly todestination device 14 in real-time.

The encoded video data may be modulated according to a communicationstandard, such as a wireless communication protocol, and transmitted todestination device 14. The communication medium may comprise anywireless or wired communication medium, such as a radio frequency (RF)spectrum or one or more physical transmission lines. The communicationmedium may form part of a packet-based network, such as a local areanetwork, a wide-area network, or a global network such as the Internet.The communication medium may include routers, switches, base stations,or any other equipment that may be useful to facilitate communicationfrom source device 12 to destination device 14.

In some examples, encoded data may be output from output interface 22 toa storage device. Similarly, encoded data may be accessed from thestorage device by input interface. The storage device may include any ofa variety of distributed or locally accessed data storage media such asa hard drive, Blu-ray discs, DVDs, CD-ROMs, flash memory, volatile ornon-volatile memory, or any other suitable digital storage media forstoring encoded video data. In a further example, the storage device maycorrespond to a file server or another intermediate storage device thatmay store the encoded video generated by source device 12.

Destination device 14 may access stored video data from the storagedevice via streaming or download. The file server may be any type ofserver capable of storing encoded video data and transmitting thatencoded video data to the destination device 14. Example file serversinclude a web server (e.g., for a website), an FTP server, networkattached storage (NAS) devices, or a local disk drive. Destinationdevice 14 may access the encoded video data through any standard dataconnection, including an Internet connection. This may include awireless channel (e.g., a Wi-Fi connection), a wired connection (e.g.,DSL, cable modem, etc.), or a combination of both that is suitable foraccessing encoded video data stored on a file server. The transmissionof encoded video data from the storage device may be a streamingtransmission, a download transmission, or a combination thereof.

The techniques of this disclosure are not necessarily limited towireless applications or settings. The techniques may be applied tovideo coding in support of any of a variety of multimedia applications,such as over-the-air television broadcasts, cable televisiontransmissions, satellite television transmissions, Internet streamingvideo transmissions, such as dynamic adaptive streaming over HTTP(DASH), digital video that is encoded onto a data storage medium,decoding of digital video stored on a data storage medium, or otherapplications. In some examples, system 10 may be configured to supportone-way or two-way video transmission to support applications such asvideo streaming, video playback, video broadcasting, and/or videotelephony.

In the example of FIG. 1, source device 12 includes video source 18,video encoder 20, and output interface 22. Destination device 14includes input interface 28, video decoder 30, and display device 32. Inaccordance with this disclosure, video encoder 20 of source device 12may be configured to apply the techniques for motion vector predictionin multiview coding. In other examples, a source device and adestination device may include other components or arrangements. Forexample, source device 12 may receive video data from an external videosource 18, such as an external camera. Likewise, destination device 14may interface with an external display device, rather than including anintegrated display device.

The illustrated system 10 of FIG. 1 is merely one example. Techniquesfor motion vector prediction in multiview coding may be performed by anydigital video encoding and/or decoding device. Although generally thetechniques of this disclosure are performed by a video encoding device,the techniques may also be performed by a video encoder/decoder,typically referred to as a “CODEC.” Moreover, the techniques of thisdisclosure may also be performed by a video preprocessor. Source device12 and destination device 14 are merely examples of such coding devicesin which source device 12 generates coded video data for transmission todestination device 14. In some examples, devices 12, 14 may operate in asubstantially symmetrical manner such that each of devices 12, 14include video encoding and decoding components. Hence, system 10 maysupport one-way or two-way video transmission between video devices 12,14, e.g., for video streaming, video playback, video broadcasting, orvideo telephony.

Video source 18 of source device 12 may include a video capture device,such as a video camera, a video archive containing previously capturedvideo, and/or a video feed interface to receive video from a videocontent provider. As a further alternative, video source 18 may generatecomputer graphics-based data as the source video, or a combination oflive video, archived video, and computer-generated video. In some cases,if video source 18 is a video camera, source device 12 and destinationdevice 14 may form so-called camera phones or video phones. As mentionedabove, however, the techniques described in this disclosure may beapplicable to video coding in general, and may be applied to wirelessand/or wired applications. In each case, the captured, pre-captured, orcomputer-generated video may be encoded by video encoder 20. The encodedvideo information may then be output by output interface 22 onto acomputer-readable medium 16.

Computer-readable medium 16 may include transient media, such as awireless broadcast or wired network transmission, or storage media (thatis, non-transitory storage media), such as a hard disk, flash drive,compact disc, digital video disc, Blu-ray disc, or othercomputer-readable media. In some examples, a network server (not shown)may receive encoded video data from source device 12 and provide theencoded video data to destination device 14, e.g., via networktransmission. Similarly, a computing device of a medium productionfacility, such as a disc stamping facility, may receive encoded videodata from source device 12 and produce a disc containing the encodedvideo data. Therefore, computer-readable medium 16 may be understood toinclude one or more computer-readable media of various forms, in variousexamples.

Input interface 28 of destination device 14 receives information fromcomputer-readable medium 16. The information of computer-readable medium16 may include syntax information defined by video encoder 20, which isalso used by video decoder 30, that includes syntax elements thatdescribe characteristics and/or processing of blocks and other codedunits, e.g., GOPs. Display device 32 displays the decoded video data toa user, and may comprise any of a variety of display devices such as acathode ray tube (CRT), a liquid crystal display (LCD), a plasmadisplay, an organic light emitting diode (OLED) display, or another typeof display device.

Video encoder 20 and video decoder 30 may operate according to a videocoding standard, such as the High Efficiency Video Coding (HEVC)standard presently under development, and may conform to the HEVC TestModel (HM). Alternatively, video encoder 20 and video decoder 30 mayoperate according to other proprietary or industry standards, such asthe ITU-T H.264 standard, alternatively referred to as MPEG-4, Part 10,Advanced Video Coding (AVC), or extensions of such standards. Thetechniques of this disclosure, however, are not limited to anyparticular coding standard. Other examples of video coding standardsinclude MPEG-2 and ITU-T H.263. Although not shown in FIG. 1, in someaspects, video encoder 20 and video decoder 30 may each be integratedwith an audio encoder and decoder, and may include appropriate MUX-DEMUXunits, or other hardware and software, to handle encoding of both audioand video in a common data stream or separate data streams. Ifapplicable, MUX-DEMUX units may conform to the ITU H.223 multiplexerprotocol, or other protocols such as the user datagram protocol (UDP).

The ITU-T H.264/MPEG-4 (AVC) standard was formulated by the ITU-T VideoCoding Experts Group (VCEG) together with the ISO/IEC Moving PictureExperts Group (MPEG) as the product of a collective partnership known asthe Joint Video Team (JVT). In some aspects, the techniques described inthis disclosure may be applied to devices that generally conform to theH.264 standard. The H.264 standard is described in ITU-T RecommendationH.264, Advanced Video Coding for generic audiovisual services, by theITU-T Study Group, and dated March, 2005, which may be referred toherein as the H.264 standard or H.264 specification, or the H.264/AVCstandard or specification. The Joint Video Team (JVT) continues to workon extensions to H.264/MPEG-4 AVC.

The JCT-VC is working on development of the HEVC standard. The HEVCstandardization efforts are based on an evolving model of a video codingdevice referred to as the HEVC Test Model (HM). The HM presumes severaladditional capabilities of video coding devices relative to existingdevices according to, e.g., ITU-T H.264/AVC. For example, whereas H.264provides nine intra-prediction encoding modes, the HM may provide asmany as thirty-three intra-prediction encoding modes.

In general, the working model of the HM describes that a video picture(or “frame”) may be divided into a sequence of treeblocks or largestcoding units (LCU) that include both luma and chroma samples. Syntaxdata within a bitstream may define a size for the LCU, which is alargest coding unit in terms of the number of pixels. A slice includes anumber of consecutive treeblocks in coding order. A picture may bepartitioned into one or more slices. Each treeblock may be split intocoding units (CUs) according to a quadtree. In general, a quadtree datastructure includes one node per CU, with a root node corresponding tothe treeblock. If a CU is split into four sub-CUs, the nodecorresponding to the CU includes four leaf nodes, each of whichcorresponds to one of the sub-CUs.

Each node of the quadtree data structure may provide syntax data for thecorresponding CU. For example, a node in the quadtree may include asplit flag, indicating whether the CU corresponding to the node is splitinto sub-CUs. Syntax elements for a CU may be defined recursively, andmay depend on whether the CU is split into sub-CUs. If a CU is not splitfurther, it is referred as a leaf-CU. In this disclosure, four sub-CUsof a leaf-CU will also be referred to as leaf-CUs even if there is noexplicit splitting of the original leaf-CU. For example, if a CU at16×16 size is not split further, the four 8×8 sub-CUs will also bereferred to as leaf-CUs although the 16×16 CU was never split.

A CU has a similar purpose as a macroblock of the H.264 standard, exceptthat a CU does not have a size distinction. For example, a treeblock maybe split into four child nodes (also referred to as sub-CUs), and eachchild node may in turn be a parent node and be split into another fourchild nodes. A final, unsplit child node, referred to as a leaf node ofthe quadtree, comprises a coding node, also referred to as a leaf-CU.Syntax data associated with a coded bitstream may define a maximumnumber of times a treeblock may be split, referred to as a maximum CUdepth, and may also define a minimum size of the coding nodes.Accordingly, a bitstream may also define a smallest coding unit (SCU).This disclosure uses the term “block” to refer to any of a CU, PU, orTU, in the context of HEVC, or similar data structures in the context ofother standards (e.g., macroblocks and sub-blocks thereof in H.264/AVC).

A CU includes a coding node and prediction units (PUs) and transformunits (TUs) associated with the coding node. A size of the CUcorresponds to a size of the coding node and must be square in shape.The size of the CU may range from 8×8 pixels up to the size of thetreeblock with a maximum of 64×64 pixels or greater. Each CU may containone or more PUs and one or more TUs. Syntax data associated with a CUmay describe, for example, partitioning of the CU into one or more PUs.Partitioning modes may differ between whether the CU is skip or directmode encoded, intra-prediction mode encoded, or inter-prediction modeencoded. PUs may be partitioned to be non-square in shape. Syntax dataassociated with a CU may also describe, for example, partitioning of theCU into one or more TUs according to a quadtree. A TU can be square ornon-square (e.g., rectangular) in shape.

The HEVC standard allows for transformations according to TUs, which maybe different for different CUs. The TUs are typically sized based on thesize of PUs within a given CU defined for a partitioned LCU, althoughthis may not always be the case. The TUs are typically the same size orsmaller than the PUs. In some examples, residual samples correspondingto a CU may be subdivided into smaller units using a quadtree structureknown as “residual quad tree” (RQT). The leaf nodes of the RQT may bereferred to as transform units (TUs). Pixel difference values associatedwith the TUs may be transformed to produce transform coefficients, whichmay be quantized.

A leaf-CU may include one or more prediction units (PUs). In general, aPU represents a spatial area corresponding to all or a portion of thecorresponding CU, and may include data for retrieving a reference samplefor the PU. Moreover, a PU includes data related to prediction. Forexample, when the PU is intra-mode encoded, data for the PU may beincluded in a residual quadtree (RQT), which may include data describingan intra-prediction mode for a TU corresponding to the PU. As anotherexample, when the PU is inter-mode encoded, the PU may include datadefining one or more motion vectors for the PU. The data defining themotion vector for a PU may describe, for example, a horizontal componentof the motion vector, a vertical component of the motion vector, aresolution for the motion vector (e.g., one-quarter pixel precision orone-eighth pixel precision), a reference picture to which the motionvector points, and/or a reference picture list (e.g., List 0, List 1, orList C) for the motion vector.

A leaf-CU having one or more PUs may also include one or more transformunits (TUs). The transform units may be specified using an RQT (alsoreferred to as a TU quadtree structure), as discussed above. Forexample, a split flag may indicate whether a leaf-CU is split into fourtransform units. Then, each transform unit may be split further intofurther sub-TUs. When a TU is not split further, it may be referred toas a leaf-TU. Generally, for intra coding, all the leaf-TUs belonging toa leaf-CU share the same intra prediction mode. That is, the sameintra-prediction mode is generally applied to calculate predicted valuesfor all TUs of a leaf-CU. For intra coding, a video encoder 20 maycalculate a residual value for each leaf-TU using the intra predictionmode, as a difference between the portion of the CU corresponding to theTU and the original block. A TU is not necessarily limited to the sizeof a PU. Thus, TUs may be larger or smaller than a PU. For intra coding,a PU may be collocated with a corresponding leaf-TU for the same CU. Insome examples, the maximum size of a leaf-TU may correspond to the sizeof the corresponding leaf-CU.

Moreover, TUs of leaf-CUs may also be associated with respectivequadtree data structures, referred to as residual quadtrees (RQTs). Thatis, a leaf-CU may include a quadtree indicating how the leaf-CU ispartitioned into TUs. The root node of a TU quadtree generallycorresponds to a leaf-CU, while the root node of a CU quadtree generallycorresponds to a treeblock (or LCU). TUs of the RQT that are not splitare referred to as leaf-TUs. In general, this disclosure uses the termsCU and TU to refer to leaf-CU and leaf-TU, respectively, unless notedotherwise.

A video sequence typically includes a series of pictures. As describedherein, “picture” and “frame” may be used interchangeably. That is,picture containing video data may be referred to as video frame, orsimply “frame.” A group of pictures (GOP) generally comprises a seriesof one or more of the video pictures. A GOP may include syntax data in aheader of the GOP, a header of one or more of the pictures, orelsewhere, that describes a number of pictures included in the GOP. Eachslice of a picture may include slice syntax data that describes anencoding mode for the respective slice. Video encoder 20 typicallyoperates on video blocks within individual video slices in order toencode the video data. A video block may correspond to a coding nodewithin a CU. The video blocks may have fixed or varying sizes, and maydiffer in size according to a specified coding standard.

As an example, the HM supports prediction in various PU sizes. Assumingthat the size of a particular CU is 2N×2N, the HM supportsintra-prediction in PU sizes of 2N×2N or N×N, and inter-prediction insymmetric PU sizes of 2N×2N, 2N×N, N×2N, or N×N. The HM also supportsasymmetric partitioning for inter-prediction in PU sizes of 2N×nU,2N×nD, nL×2N, and nR×2N. In asymmetric partitioning, one direction of aCU is not partitioned, while the other direction is partitioned into 25%and 75%. The portion of the CU corresponding to the 25% partition isindicated by an “n” followed by an indication of “Up”, “Down,” “Left,”or “Right.” Thus, for example, “2N×nU” refers to a 2N×2N CU that ispartitioned horizontally with a 2N×0.5N PU on top and a 2N×1.5N PU onbottom.

In this disclosure, “N×N” and “N by N” may be used interchangeably torefer to the pixel dimensions of a video block in terms of vertical andhorizontal dimensions, e.g., 16×16 pixels or 16 by 16 pixels. Ingeneral, a 16×16 block will have 16 pixels in a vertical direction(y=16) and 16 pixels in a horizontal direction (x=16). Likewise, an N×Nblock generally has N pixels in a vertical direction and N pixels in ahorizontal direction, where N represents a nonnegative integer value.The pixels in a block may be arranged in rows and columns. Moreover,blocks need not necessarily have the same number of pixels in thehorizontal direction as in the vertical direction. For example, blocksmay comprise N×M pixels, where M is not necessarily equal to N.

Following intra-predictive or inter-predictive coding using the PUs of aCU, video encoder 20 may calculate residual data for the TUs of the CU.The PUs may comprise syntax data describing a method or mode ofgenerating predictive pixel data in the spatial domain (also referred toas the pixel domain) and the TUs may comprise coefficients in thetransform domain following application of a transform, e.g., a discretecosine transform (DCT), an integer transform, a wavelet transform, or aconceptually similar transform to residual video data. The residual datamay correspond to pixel differences between pixels of the unencodedpicture and prediction values corresponding to the PUs. Video encoder 20may form the TUs including the residual data for the CU, and thentransform the TUs to produce transform coefficients for the CU.

Following any transforms to produce transform coefficients, videoencoder 20 may perform quantization of the transform coefficients.Quantization generally refers to a process in which transformcoefficients are quantized to possibly reduce the amount of data used torepresent the coefficients, providing further compression. Thequantization process may reduce the bit depth associated with some orall of the coefficients. For example, an n-bit value may be rounded downto an m-bit value during quantization, where n is greater than m.

Following quantization, the video encoder may scan the transformcoefficients, producing a one-dimensional vector from thetwo-dimensional matrix including the quantized transform coefficients.The scan may be designed to place higher energy (and therefore lowerfrequency) coefficients at the front of the array and to place lowerenergy (and therefore higher frequency) coefficients at the back of thearray. In some examples, video encoder 20 may utilize a predefined scanorder to scan the quantized transform coefficients to produce aserialized vector that can be entropy encoded. In other examples, videoencoder 20 may perform an adaptive scan. After scanning the quantizedtransform coefficients to form a one-dimensional vector, video encoder20 may entropy encode the one-dimensional vector, e.g., according tocontext-adaptive variable length coding (CAVLC), context-adaptive binaryarithmetic coding (CABAC), syntax-based context-adaptive binaryarithmetic coding (SBAC), Probability Interval Partitioning Entropy(PIPE) coding or another entropy encoding methodology. Video encoder 20may also entropy encode syntax elements associated with the encodedvideo data for use by video decoder 30 in decoding the video data.

To perform CABAC, video encoder 20 may assign a context within a contextmodel to a symbol to be transmitted. The context may relate to, forexample, whether neighboring values of the symbol are non-zero or not.To perform CAVLC, video encoder 20 may select a variable length code fora symbol to be transmitted. Codewords in VLC may be constructed suchthat relatively shorter codes correspond to more probable symbols, whilelonger codes correspond to less probable symbols. In this way, the useof VLC may achieve a bit savings over, for example, using equal-lengthcodewords for each symbol to be transmitted. The probabilitydetermination may be based on a context assigned to the symbol.

Video encoder 20 may further send syntax data, such as block-basedsyntax data, picture-based syntax data, and GOP-based syntax data, tovideo decoder 30, e.g., in a picture header, a block header, a sliceheader, or a GOP header. The GOP syntax data may describe a number ofpictures in the respective GOP, and the picture syntax data may indicatean encoding/prediction mode used to encode the corresponding picture.

Video encoder 20 and video decoder 30 each may be implemented as any ofa variety of suitable encoder or decoder circuitry, as applicable, suchas one or more microprocessors, digital signal processors (DSPs),application specific integrated circuits (ASICs), field programmablegate arrays (FPGAs), discrete logic circuitry, software, hardware,firmware or any combinations thereof. Each of video encoder 20 and videodecoder 30 may be included in one or more encoders or decoders, eitherof which may be integrated as part of a combined video encoder/decoder(CODEC). A device including video encoder 20 and/or video decoder 30 maycomprise an integrated circuit, a microprocessor, and/or a wirelesscommunication device, such as a cellular telephone.

FIG. 2 is a block diagram illustrating an example video encoder 20 thatmay implement the techniques described in this disclosure for predictingmotion vectors in multiview coding. Video encoder 20 may perform intra-and inter-coding of video blocks within video slices. Intra-codingrelies on spatial prediction to reduce or remove spatial redundancy invideo within a given picture. Inter-coding relies on temporal predictionto reduce or remove temporal redundancy in video within adjacentpictures or pictures of a video sequence. Intra-mode (I mode) may referto any of several spatial based compression modes. Inter-modes, such asuni-directional prediction (P mode) or bi-prediction (B mode), may referto any of several temporal-based compression modes.

As shown in FIG. 2, video encoder 20 receives video data to be encoded.In the example of FIG. 2, video encoder 20 includes a mode select unit40, summer 50, transform unit 52, quantization unit 54, entropy encodingunit 56, and reference picture memory 64. Mode select unit 40, in turn,includes motion estimation unit 42, motion compensation unit 44, intraprediction unit 46, and partition unit 48. For video blockreconstruction, video encoder 20 also includes inverse quantization unit58, inverse transform unit 60, and summer 62. A deblocking filter (notshown in FIG. 2) may also be included to filter block boundaries toremove blockiness artifacts from reconstructed video. If desired, thedeblocking filter would typically filter the output of summer 62.Additional loop filters (in loop or post loop) may also be used inaddition to the deblocking filter. Such filters are not shown forbrevity, but if desired, may filter the output of summer 50 (as anin-loop filter).

During the encoding process, video encoder 20 receives a picture orslice to be coded. The picture or slice may be divided into multiplevideo blocks. Motion estimation unit 42 and motion compensation unit 44perform inter-predictive coding of the received video block relative toone or more blocks in one or more reference pictures to provide temporalcompression. Intra-prediction unit 46 may alternatively performintra-predictive coding of the received video block relative to one ormore neighboring blocks in the same picture or slice as the block to becoded to provide spatial compression. Video encoder 20 may performmultiple coding passes, e.g., to select an appropriate coding mode foreach block of video data.

Moreover, partition unit 48 may partition blocks of video data intosub-blocks, based on evaluation of previous partitioning schemes inprevious coding passes. For example, partition unit 48 may initiallypartition a picture or slice into LCUs, and partition each of the LCUsinto sub-CUs based on rate-distortion analysis (e.g., rate-distortionoptimization). Mode select unit 40 may further produce a quadtree datastructure indicative of partitioning of an LCU into sub-CUs. Leaf-nodeCUs of the quadtree may include one or more PUs and one or more TUs.

Mode select unit 40 may select one of the coding modes, intra or inter,e.g., based on error results, and provides the resulting intra- orinter-coded block to summer 50 to generate residual block data and tosummer 62 to reconstruct the encoded block for use as a referencepicture. Mode select unit 40 also provides syntax elements, such asmotion vectors, intra-mode indicators, partition information, and othersuch syntax information, to entropy coding unit 56.

Motion estimation unit 42, motion vector prediction unit 43, and motioncompensation unit 44 may be highly integrated, but are illustratedseparately for conceptual purposes. Motion estimation, performed bymotion estimation unit 42, is the process of generating motion vectors,which estimate motion for video blocks. A motion vector, for example,may indicate the displacement of a PU of a video block within a currentpicture relative to a predictive block within a reference picture (orother coded unit) relative to the current block being coded within thecurrent picture (or other coded unit).

A predictive block is a block that is found to closely match the blockto be coded, in terms of pixel difference, which may be determined bysum of absolute difference (SAD), sum of square difference (SSD), orother difference metrics. In some examples, video encoder 20 maycalculate values for sub-integer pixel positions of reference picturesstored in reference picture memory 64, which may also be referred to asa reference picture buffer. For example, video encoder 20 mayinterpolate values of one-quarter pixel positions, one-eighth pixelpositions, or other fractional pixel positions of the reference picture.Therefore, motion estimation unit 42 may perform a motion searchrelative to the full pixel positions and fractional pixel positions andoutput a motion vector with fractional pixel precision.

Motion estimation unit 42 calculates a motion vector for a PU of a videoblock in an inter-coded slice by comparing the position of the PU to theposition of a predictive block of a reference picture. Accordingly, ingeneral, data for a motion vector may include a reference picture list,an index into the reference picture list (ref_idx), a horizontalcomponent, and a vertical component. The reference picture may beselected from a first reference picture list (List 0), a secondreference picture list (List 1), or a combined reference picture list(List c), each of which identify one or more reference pictures storedin reference picture memory 64.

Motion estimation unit 42 may generate and send a motion vector thatidentifies the predictive block of the reference picture to entropyencoding unit 56 and motion compensation unit 44. That is, motionestimation unit 42 may generate and send motion vector data thatidentifies the reference picture list containing the predictive block,an index into the reference picture list identifying the picture of thepredictive block, and a horizontal and vertical component to locate thepredictive block within the identified picture.

In some examples, rather than sending the actual motion vector for acurrent PU, motion vector prediction unit 43 may predict the motionvector to further reduce the amount of data needed to communicate themotion vector. In this case, rather than encoding and communicating themotion vector itself, motion vector prediction unit 43 may generate amotion vector difference (MVD) relative to a known (or knowable) motionvector. The known motion vector, which may be used with the MVD todefine the current motion vector, can be defined by a so-called motionvector predictor (MVP). In general, to be a valid MVP, the motion vectorbeing used for prediction must point to the same reference picture asthe motion vector currently being coded.

In some examples, as described in greater detail with respect to FIG. 5below, motion vector prediction unit 43 may build a motion vectorpredictor candidate list that includes several neighboring blocks inspatial and/or temporal directions as candidates for MVP. According toaspects of this disclosure, as described in greater detail below, motionvector predictor candidates may also be identified in pictures ofdifferent views (e.g., in multiview coding). When multiple motion vectorpredictor candidates are available (from multiple candidate blocks),motion vector prediction unit 43 may determine a motion vector predictorfor a current block according to predetermined selection criteria. Forexample, motion vector prediction unit 43 may select the most accuratepredictor from the candidate set based on analysis of encoding rate anddistortion (e.g., using a rate-distortion cost analysis or other codingefficiency analysis). In other examples, motion vector prediction unit43 may generate an average of the motion vector predictor candidates.Other methods of selecting a motion vector predictor are also possible.

Upon selecting a motion vector predictor, motion vector prediction unit43 may determine a motion vector predictor index (mvp_flag), which maybe used to inform a video decoder (e.g., such as video decoder 30) whereto locate the MVP in a reference picture list containing MVP candidateblocks. Motion vector prediction unit 43 may also determine the MVDbetween the current block and the selected MVP. The MVP index and MVDmay be used to reconstruct the motion vector.

In some examples, motion vector prediction unit 43 may instead implementa so-called “merge mode,” in which motion vector prediction unit 43 may“merge” motion information (such as motion vectors, reference pictureindexes, prediction directions, or other information) of predictivevideo block with a current video block. Accordingly, with respect tomerge mode, a current video block inherits the motion information fromanother known (or knowable) video block. Motion vector prediction unit43 may build a merge mode candidate list that includes severalneighboring blocks in spatial and/or temporal directions as candidatesfor merge mode. Motion vector prediction unit 43 may determine an indexvalue (e.g., merge_idx), which may be used to inform a video decoder(e.g., such as video decoder 30) where to locate the merging video blockin a reference picture list containing merging candidate blocks.

According to aspects of this disclosure, motion vector prediction unit43 may identify a motion vector predictor, e.g., for generating an MVDor merging, in multiview coding. For example, motion vector predictionunit 43 may identify a disparity motion vector from a block in adifferent view component than a current block to predict the motionvector for the current block. In other examples, motion vectorprediction unit 43 may identify a temporal motion vector from a block ina different view component than a current block to predict the motionvector for the current block.

Regarding disparity motion vector prediction, motion vector predictionunit 43 may identify a disparity motion vector candidate from acandidate block to predict a motion vector for a video block currentlybeing coded (referred to as “the current block”). The current block maybe located in the same picture as the candidate block (e.g., spatiallyneighbor the candidate block), or may be located in another picturewithin the same view as the candidate block. In some examples, motionvector prediction unit 43 may identify a motion vector predictor thatrefers to a reference picture in different view than a motion vector forthe current block. In such instances, according to the techniques ofthis disclosure, motion vector prediction unit 43 may scale the motionvector predictor based on a difference in camera locations between thetwo views (e.g., the view referred to by the motion vector predictor andthe view referred to by the current motion vector). For example, motionvector prediction unit 43 may scale the disparity motion vectorpredictor according to a difference between the two views. In someexamples, the difference between the two views may be represented by adifference between view identifiers (view_id) associated with the views.

Regarding temporal motion vector prediction, motion vector predictionunit 43 may identify a temporal motion vector candidate from a candidateblock in a different view than a current block to predict a motionvector for the current block. For example, motion vector prediction unit43 may identify a temporal motion vector predictor candidate in a firstview that refers to a block in a picture at another temporal location ofthe first view. According to aspects of this disclosure, motion vectorprediction unit 43 may use the identified temporal motion vectorpredictor candidate to predict a motion vector associated with a currentblock in a second, different view. The candidate block (which includesthe motion vector predictor candidate) and the current block may beco-located. However, the relative location of the candidate block may beoffset from the current block, due to a disparity between the two views.

According to aspects of this disclosure, motion vector prediction unit43 may generate an MVP index (mvp_flag) and MVD, or may generate a mergeindex (merge_idx). For example, motion vector prediction unit 43 maygenerate a list of MVP or merge candidates. According to aspects of thisdisclosure, the MVP and/or merge candidates include one or more videoblocks located in a different view than a video block currently beingdecoded.

Motion compensation, performed by motion compensation unit 44, mayinvolve fetching or generating the predictive block based on the motionvector determined by motion estimation unit 42 and/or the informationfrom motion vector prediction unit 43. Again, motion estimation unit 42,motion vector prediction unit 43, and motion compensation unit 44 may befunctionally integrated, in some examples. Upon receiving the motionvector for the PU of the current video block, motion compensation unit44 may locate the predictive block to which the motion vector points inone of the reference picture lists.

Summer 50 forms a residual video block by subtracting pixel values ofthe predictive block from the pixel values of the current video blockbeing coded, forming pixel difference values, as discussed below. Ingeneral, motion estimation unit 42 performs motion estimation relativeto luma components, and motion compensation unit 44 uses motion vectorscalculated based on the luma components for both chroma components andluma components. Mode select unit 40 may also generate syntax elementsassociated with the video blocks and the video slice for use by videodecoder 30 in decoding the video blocks of the video slice.

Intra-prediction unit 46 may intra-predict a current block, as analternative to the inter-prediction performed by motion estimation unit42 and motion compensation unit 44, as described above. In particular,intra-prediction unit 46 may determine an intra-prediction mode to useto encode a current block. In some examples, intra-prediction unit 46may encode a current block using various intra-prediction modes, e.g.,during separate encoding passes, and intra-prediction unit 46 (or modeselect unit 40, in some examples) may select an appropriateintra-prediction mode to use from the tested modes.

For example, intra-prediction unit 46 may calculate rate-distortionvalues using a rate-distortion analysis for the various testedintra-prediction modes, and select the intra-prediction mode having thebest rate-distortion characteristics among the tested modes.Rate-distortion analysis generally determines an amount of distortion(or error) between an encoded block and an original, unencoded blockthat was encoded to produce the encoded block, as well as a bitrate(that is, a number of bits) used to produce the encoded block.Intra-prediction unit 46 may calculate ratios from the distortions andrates for the various encoded blocks to determine which intra-predictionmode exhibits the best rate-distortion value for the block.

After selecting an intra-prediction mode for a block, intra-predictionunit 46 may provide information indicative of the selectedintra-prediction mode for the block to entropy coding unit 56. Entropycoding unit 56 may encode the information indicating the selectedintra-prediction mode. Video encoder 20 may include in the transmittedbitstream configuration data, which may include a plurality ofintra-prediction mode index tables and a plurality of modifiedintra-prediction mode index tables (also referred to as codeword mappingtables), definitions of encoding contexts for various blocks, andindications of a most probable intra-prediction mode, anintra-prediction mode index table, and a modified intra-prediction modeindex table to use for each of the contexts.

Video encoder 20 forms a residual video block by subtracting theprediction data from mode select unit 40 from the original video blockbeing coded. Summer 50 represents the component or components thatperform this subtraction operation. Transform processing unit 52 appliesa transform, such as a discrete cosine transform (DCT) or a conceptuallysimilar transform, to the residual block, producing a video blockcomprising residual transform coefficient values. Transform processingunit 52 may perform other transforms which are conceptually similar toDCT. Wavelet transforms, integer transforms, sub-band transforms orother types of transforms could also be used. In any case, transformprocessing unit 52 applies the transform to the residual block,producing a block of residual transform coefficients. The transform mayconvert the residual information from a pixel value domain to atransform domain, such as a frequency domain.

Transform processing unit 52 may send the resulting transformcoefficients to quantization unit 54. Quantization unit 54 quantizes thetransform coefficients to further reduce bit rate. The quantizationprocess may reduce the bit depth associated with some or all of thecoefficients. The degree of quantization may be modified by adjusting aquantization parameter. In some examples, quantization unit 54 may thenperform a scan of the matrix including the quantized transformcoefficients. Alternatively, entropy encoding unit 56 may perform thescan.

Following quantization, entropy coding unit 56 entropy codes thequantized transform coefficients. For example, entropy coding unit 56may perform context adaptive variable length coding (CAVLC), contextadaptive binary arithmetic coding (CABAC), syntax-based context-adaptivebinary arithmetic coding (SBAC), probability interval partitioningentropy (PIPE) coding or another entropy coding technique. In the caseof context-based entropy coding, context may be based on neighboringblocks. Following the entropy coding by entropy coding unit 56, theencoded bitstream may be transmitted to another device (e.g., videodecoder 30) or archived for later transmission or retrieval.

Inverse quantization unit 58 and inverse transform unit 60 apply inversequantization and inverse transformation, respectively, to reconstructthe residual block in the pixel domain, e.g., for later use as areference block. Motion compensation unit 44 may calculate a referenceblock by adding the residual block to a predictive block of one of thepictures of reference picture memory 64. Motion compensation unit 44 mayalso apply one or more interpolation filters to the reconstructedresidual block to calculate sub-integer pixel values for use in motionestimation. Summer 62 adds the reconstructed residual block to themotion compensated prediction block produced by motion compensation unit44 to produce a reconstructed video block for storage in referencepicture memory 64. The reconstructed video block may be used by motionestimation unit 42 and motion compensation unit 44 as a reference blockto inter-code a block in a subsequent picture.

FIG. 3 is a block diagram illustrating an example video decoder 30 thatmay implement the techniques described in this disclosure for predictingmotion vectors in multiview coding. In the example of FIG. 3, videodecoder 30 includes an entropy decoding unit 80, prediction unit 81,inverse quantization unit 86, inverse transformation unit 88, summer 90,and reference picture memory 92. Prediction unit 81 includes motioncompensation unit 82 and intra prediction unit 84.

During the decoding process, video decoder 30 receives an encoded videobitstream that represents video blocks of an encoded video slice andassociated syntax elements from video encoder 20. Entropy decoding unit80 of video decoder 30 entropy decodes the bitstream to generatequantized coefficients, motion vectors, and other syntax elements.Entropy decoding unit 80 forwards the motion vectors and other syntaxelements to prediction unit 81. Video decoder 30 may receive the syntaxelements at the video slice level and/or the video block level.

For example, by way of background, video decoder 30 may receivecompressed video data that has been compressed for transmission via anetwork into so-called “network abstraction layer units” or NAL units.Each NAL unit may include a header that identifies a type of data storedto the NAL unit. There are two types of data that are commonly stored toNAL units. The first type of data stored to a NAL unit is video codinglayer (VCL) data, which includes the compressed video data. The secondtype of data stored to a NAL unit is referred to as non-VCL data, whichincludes additional information such as parameter sets that defineheader data common to a large number of NAL units and supplementalenhancement information (SEI).

For example, parameter sets may contain the sequence-level headerinformation (e.g., in sequence parameter sets (SPS)) and theinfrequently changing picture-level header information (e.g., in pictureparameter sets (PPS)). The infrequently changing information containedin the parameter sets does not need to be repeated for each sequence orpicture, thereby improving coding efficiency. In addition, the use ofparameter sets enables out-of-band transmission of header information,thereby avoiding the need of redundant transmissions for errorresilience.

When the video slice is coded as an intra-coded (I) slice, intraprediction unit 84 of prediction unit 81 may generate prediction datafor a video block of the current video slice based on a signaled intraprediction mode and data from previously decoded blocks of the currentpicture. When the picture is coded as an inter-coded (i.e., B, P or GPB)slice, motion compensation unit 82 of prediction unit 81 producespredictive blocks for a video block of the current video slice based onthe motion vectors and other syntax elements received from entropydecoding unit 80. The predictive blocks may be produced from one of thereference pictures within one of the reference picture lists. Videodecoder 30 may construct the reference picture lists, List 0 and List 1,using default construction techniques based on reference pictures storedin reference picture memory 92.

Motion compensation unit 82 determines prediction information for avideo block of the current video slice by parsing the motion vectors andother syntax elements, and uses the prediction information to producethe predictive blocks for the current video block being decoded. Forexample, motion compensation unit 82 uses some of the received syntaxelements to determine a prediction mode (e.g., intra- orinter-prediction) used to code the video blocks of the video slice, aninter-prediction slice type (e.g., B slice, P slice, or GPB slice),construction information for one or more of the reference picture listsfor the slice, motion vectors for each inter-encoded video block of theslice, inter-prediction status for each inter-coded video block of theslice, and other information to decode the video blocks in the currentvideo slice. In some examples, motion compensation unit 82 may receivecertain motion information from motion vector prediction unit 83.

According to aspects of this disclosure, motion vector prediction unit83 may receive prediction data indicating where to retrieve motioninformation for a current block. For example, motion vector predictionunit 83 may receive motion vector prediction information such as an MVPindex (mvp_flag), MVD, merge flag (merge_flag), and/or merge index(merge_idx) and use such information to identify motion information usedto predict a current block. That is, as noted above with respect tovideo encoder 20, according to aspects of this disclosure, motion vectorprediction unit 83 may receive an MVP index (mvp_flag) and MVD, and usesuch information to determine a motion vector used to predict a currentblock. Motion vector prediction unit 83 may generate a list of MVP ormerge candidates. According to aspects of this disclosure, the MVPand/or merge candidates may include one or more video blocks located ina different view than a video block currently being decoded.

Motion vector prediction unit 83 may use an MVP or merge index toidentify the motion information used to predict the motion vector of acurrent block. That is, for example, motion vector prediction unit 83may identify an MVP from a list of reference picture using the MVP index(mvp_flag). Motion vector prediction unit 83 may combine the identifiedMVP with a received MVD to determine the motion vector for the currentblock. In other examples, motion vector prediction unit 83 may identifya merge candidate from a list of reference pictures using a merge index(merge_idx) to determine motion information for the current block. Inany event, after determining motion information for the current block,motion vector prediction unit 83 may generate the predictive block forthe current block.

According to aspects of this disclosure, motion vector prediction unit83 may determine a motion vector predictor in multiview coding. Forexample, motion vector prediction unit 83 may receive informationspecifying a disparity motion vector from a block in a different viewcomponent than a current block that is used to predict the motion vectorfor the current block. In other examples, motion vector prediction unit83 may receive information identifying a temporal motion vector from ablock in a different view component than a current block that is used topredict the motion vector for the current block.

Regarding disparity motion vector prediction, motion vector predictionunit 83 may predict a disparity motion vector for the current block froma candidate block. The candidate block may be located in the samepicture as the current block (e.g., spatially neighbor the candidateblock), or may be located in another picture within the same view as thecurrent block. The candidate block may also be located in a picture of adifferent view, but in the same time instance as the current block.

For example, with respect to either MVP or merge mode, the targetpicture and reference picture for a disparity motion vector “A” of thecurrent block to be predicted are known (previously determined). Assumefor purposes of explanation that the motion vector from a candidateblock is “B.” According to aspects of this disclosure, if motion vectorB is not a disparity motion vector, motion vector prediction unit 83 mayconsider the candidate block unavailable (e.g., not available forpredicting motion vector A). That is, motion vector prediction unit 83may disable the ability to use the candidate block for purposes ofmotion vector prediction.

If the motion vector B is a disparity motion vector and the referencepicture of motion vector B belongs to the same view as that of thereference picture of disparity motion vector A, and the target pictureof motion vector B belongs to the same view as the target picture of thedisparity motion vector A, motion vector prediction unit 83 may use themotion vector B directly as a candidate predictor of motion vector A.Otherwise, motion vector prediction unit 83 may scale the disparitymotion vector B before it can be used as a candidate predictor of motionvector A. In such instances, according to the techniques of thisdisclosure, motion vector prediction unit 83 may scale the disparitymotion vector based on a view distance of motion vector A and a viewdistance of motion vector B. For example, motion vector prediction unit83 may scale disparity motion vector B by a scaling factor that is equalto view distance of motion vector A divided by view distance of motionvector B. In some examples, motion vector prediction unit 83 may performsuch scaling using the view identifiers of the reference pictures andtarget pictures.

Regarding temporal motion vector prediction, motion vector predictionunit 83 may predict a temporal motion vector for the current block froma candidate block in a different view than that of the current block.For example, motion vector prediction unit 83 may identify a temporalmotion vector predictor candidate having a target picture in a firstview and refers to a block in a reference picture at another temporallocation of the first view. According to aspects of this disclosure,motion vector prediction unit 83 may use the identified temporal motionvector predictor candidate to predict a motion vector associated withthe current block in a second, different view.

For example, with respect to either MVP or merge mode, the targetpicture and the reference picture for a temporal motion vector “A” ofthe current block to be predicted are known (previously determined).Assume for purposes of explanation that the motion vector from acandidate block is “B.” According to aspects of this disclosure, if themotion vector B from the candidate block is not a temporal motionvector, motion vector prediction unit 83 may consider the candidateblock unavailable (e.g., not available for predicting motion vector A).That is, in some examples, motion vector prediction unit 83 may disablethe ability to use the candidate block for purposes of motion vectorprediction.

If the motion vector B is a temporal motion vector, and the POC of thereference picture of motion vector B is the same as the referencepicture of the motion vector A, and the POC of the target picture ofmotion vector B is the same as the target picture of the motion vectorB, motion vector prediction unit 83 may use the motion vector B directlyas a candidate predictor of motion vector A. Otherwise, motion vectorprediction unit 83 may scale the temporal motion vector B based ontemporal distance. The candidate block (which includes the motion vectorpredictor candidate) and the current block may be co-located in adifferent view. However, the relative location of the candidate blockmay be offset from the current block, due to a disparity between the twoviews.

Inverse quantization unit 86 inverse quantizes, i.e., de-quantizes, thequantized transform coefficients provided in the bitstream and decodedby entropy decoding unit 80. The inverse quantization process mayinclude use of a quantization parameter calculated by video encoder 20for each video block in the video slice to determine a degree ofquantization and, likewise, a degree of inverse quantization that shouldbe applied.

Inverse transform unit 88 applies an inverse transform, e.g., an inverseDCT, an inverse integer transform, or a conceptually similar inversetransform process, to the transform coefficients in order to produceresidual blocks in the pixel domain. According to the aspects of thisdisclosure, inverse transform unit 88 may determine the manner in whichtransforms were applied to residual data. That is, for example, inversetransform unit 88 may determine an RQT that represents the manner inwhich transforms (e.g., DCT, integer transform, wavelet transform, orone or more other transforms) were applied to the residual luma samplesand the residual chroma samples associated with a block of receivedvideo data.

After motion compensation unit 82 generates the predictive block for thecurrent video block based on the motion vectors and other syntaxelements, video decoder 30 forms a decoded video block by summing theresidual blocks from inverse transform unit 88 with the correspondingpredictive blocks generated by motion compensation unit 82. Summer 90represents the component or components that perform this summationoperation. If desired, a deblocking filter may also be applied to filterthe decoded blocks in order to remove blockiness artifacts. Other loopfilters (either in the coding loop or after the coding loop) may also beused to smooth pixel transitions, or otherwise improve the videoquality. The decoded video blocks in a given picture are then stored inreference picture memory 92, which stores reference pictures used forsubsequent motion compensation. Reference picture memory 92 also storesdecoded video for later presentation on a display device, such asdisplay device 32 of FIG. 1.

FIG. 4 is a conceptual diagram illustrating an example MVC predictionpattern. In the example of FIG. 4, eight views are illustrated, andtwelve temporal locations are illustrated for each view. In general,each row in FIG. 4 corresponds to a view, while each column indicates atemporal location. Each of the views may be identified using a viewidentifier (“view_id”), which may be used to indicate a relative cameralocation with respect to the other views. In the example shown in FIG.4, the view IDs are indicated as “S0” through “S7”, although numericview IDs may also be used. In addition, each of the temporal locationsmay be identified using a picture order count (POC) value, whichindicates a display order of the pictures. In the example shown in FIG.4, the POC values are indicated as “T0” through “T11.”

Although MVC has a so-called base view which is decodable by H.264/AVCdecoders and stereo view pair can be supported by MVC, MVC may supportmore than two views as a 3D video input. Accordingly, a renderer of aclient having an MVC decoder may expect 3D video content with multipleviews.

Pictures in FIG. 4 are indicated using a shaded block including aletter, designating whether the corresponding picture is intra-coded(that is, an I-frame), or inter-coded in one direction (that is, as aP-frame) or in multiple directions (that is, as a B-frame). In general,predictions are indicated by arrows, where the pointed-to picture usesthe point-from object for prediction reference. For example, the P-frameof view S2 at temporal location T0 is predicted from the I-frame of viewS0 at temporal location T0.

As with single view video encoding, pictures of a multiview videosequence may be predictively encoded with respect to pictures atdifferent temporal locations. For example, the b-frame of view S0 attemporal location T1 has an arrow pointed to it from the I-frame of viewS0 at temporal location T0, indicating that the b-frame is predictedfrom the I-frame. Additionally, however, in the context of multiviewvideo encoding, pictures may be inter-view predicted. That is, a viewcomponent can use the view components in other views for reference. InMVC, for example, inter-view prediction is realized as if the viewcomponent in another view is an inter-prediction reference. Thepotential inter-view references may be signaled in the SequenceParameter Set (SPS) MVC extension and may be modified by the referencepicture list construction process, which enables flexible ordering ofthe inter-prediction or inter-view prediction references.

FIG. 4 provides various examples of inter-view prediction. Pictures ofview S1, in the example of FIG. 4, are illustrated as being predictedfrom pictures at different temporal locations of view S1, as well asinter-view predicted from pictures of pictures of views S0 and S2 at thesame temporal locations. For example, the b-frame of view S1 at temporallocation T1 is predicted from each of the B-frames of view S1 attemporal locations T0 and T2, as well as the b-frames of views S0 and S2at temporal location T1.

In the example of FIG. 4, capital “B” and lowercase “b” are intended toindicate different hierarchical relationships between pictures, ratherthan different encoding methodologies. In general, capital “B” framesare relatively higher in the prediction hierarchy than lowercase “b”frames. FIG. 4 also illustrates variations in the prediction hierarchyusing different levels of shading, where a greater amount of shading(that is, relatively darker) pictures are higher in the predictionhierarchy than those pictures having less shading (that is, relativelylighter). For example, all I-frames in FIG. 4 are illustrated with fullshading, while P-frames have a somewhat lighter shading, and B-frames(and lowercase b-frames) have various levels of shading relative to eachother, but always lighter than the shading of the P-frames and theI-frames.

In general, the prediction hierarchy is related to view order indexes,in that pictures relatively higher in the prediction hierarchy should bedecoded before decoding pictures that are relatively lower in thehierarchy, such that those pictures relatively higher in the hierarchycan be used as reference pictures during decoding of the picturesrelatively lower in the hierarchy. A view order index is an index thatindicates the decoding order of view components in an access unit. Theview order indices may be implied in a parameter set, such as an SPS.

In this manner, pictures used as reference pictures may be decodedbefore decoding the pictures that are encoded with reference to thereference pictures. A view order index is an index that indicates thedecoding order of view components in an access unit. For each view orderindex i, the corresponding view_id is signaled. The decoding of the viewcomponents follows the ascending order of the view order indexes. If allthe views are presented, then the set of view order indexes comprises aconsecutively ordered set from zero to one less than the full number ofviews.

In MVC, a subset of a whole bitstream can be extracted to form asub-bitstream which still conforms to MVC. There are many possiblesub-bitstreams that specific applications may require, based on, forexample, a service provided by a server, the capacity, support, andcapabilities of decoders of one or more clients, and/or the preferenceof one or more clients. For example, a client might require only threeviews, and there might be two scenarios. In one example, one client mayrequire smooth viewing experience and might prefer views with view_idvalues S0, S1, and S2, while another other client may require viewscalability and prefer views with view_id values S0, S2, and S4. Noteboth of these sub-bitstreams can be decoded as independent MVCbitstreams and can be supported simultaneously.

FIG. 5 is a block diagram illustrating potential motion vector predictorcandidates when performing motion vector prediction (including mergemode). That is, for block 100 currently being coded, motion information(e.g., a motion vector comprising a horizontal component and a verticalcomponent, motion vector indexes, prediction directions, or otherinformation) from neighboring blocks A₀, A₁, B₀, B₁, and B₂ may be usedto predict motion information for block 100. In addition, motioninformation associated with co-located block COL may also be used topredict motion information for block 100. The neighboring blocks A₀, A₁,B₀, B₁, and B₂ and co-located block COL, in the context of motion vectorprediction, may generally be referred to below as motion vectorpredictor candidates.

In some examples, the motion vector predictor candidates shown in FIG. 5may be identified when performing motion vector prediction (e.g.,whether generating an MVD or performing merge mode). In other examples,different candidates may be identified when performing merge mode andmotion vector prediction. That is, a video coder may identify adifferent set of motion vector predictor candidates for performing mergemode than for performing motion vector prediction.

To perform merge mode, in an example, a video encoder (such as videoencoder 20) may initially determine which motion vectors from the motionvector predictor candidates are available to merge with block 100. Thatis, in some instances, motion information from one or more of the motionvector predictor candidates may be unavailable due to, for example, themotion vector predictor candidate being intra-coded, not yet coded, ornon-existent (e.g., one or more of the motion vector predictorcandidates are located in another picture or slice). Video encoder 20may construct a motion vector predictor candidate list that includeseach of the available motion vector predictor candidate blocks.

After constructing the candidate list, video encoder 20 may select amotion vector from the candidate list to be used as the motion vectorfor current block 100. In some examples, video encoder 20 may select themotion vector from the candidate list that best matches the motionvector for block 100. That is, video encoder 20 may select the motionvector from the candidate list according to a rate distortion analysis.

Video encoder 20 may provide an indication that block 100 is encodedusing merge mode. For example, video encoder 20 may set a flag or othersyntax element indicating that the motion vector for block 100 ispredicted using merge mode. In an example, video encoder 20 may indicatethat inter prediction parameters for block 100 are inferred from amotion vector predictor candidate by setting merge_flag [x0] [y0]. Inthis example, the array indices x0, y0 may specify the location (x0, y0)of the top-left luma sample of the prediction block relative to thetop-left luma sample of the picture (or slice).

In addition, in some examples, video encoder 20 may provide an indexidentifying the merging candidate from which block 100 inherits itsmotion vector. For example, merge_idx [x0] [y0] may specify the mergingcandidate index, which identifies a picture in merging candidate listand where x0, y0 specifies the location (x0, y0) of the top-left lumasample of the prediction block relative to the top-left luma sample ofthe picture (or slice).

A video decoder (such as video decoder 30) may perform similar steps toidentify the appropriate merge candidate when decoding block 100. Forexample, video decoder 30 may receive an indication the block 100 ispredicted using merge mode. In an example, video decoder 30 may receivemerge_flag [x0][y0], where (x0, y0) specify the location of the top-leftluma sample of the prediction block relative to the top-left luma sampleof the picture (or slice).

In addition, video decoder 30 may construct a merge candidate list. Forexample, video decoder 30 may receive one or more syntax elements (e.g.,flags) indicating video blocks that are available for motion vectorprediction. Video decoder 30 may construct a merge candidate list basedon the received flags. According to some examples, video decoder 30 mayconstruct the merge candidate list (e.g., mergeCandList) according tothe following sequence:

-   -   1. A₁, if availableFlagA₁ is equal to 1    -   2. B₁, if availableFlagB₁ is equal to 1    -   3. B₀, if availableFlagB₀ is equal to 1    -   4. A₀, if availableFlagA₀ is equal to 1    -   5. B₂, if availableFlagB₂ is equal to 1    -   6. Col, if availableFlagCol is equal to 1        If several merging candidates have the same motion vectors and        the same reference indices, the merging candidates may be        removed from the list.

Video decoder 30 may identify the appropriate merge candidate accordingto a received index. For example, video decoder 30 may receive an indexidentifying the merging candidate from which block 100 inherits itsmotion vector. In an example, merge_idx [x0][y0] may specify the mergingcandidate index, which identifies a picture in merging candidate listand where x0, y0 specifies the location (x0, y0) of the top-left lumasample of the prediction block relative to the top-left luma sample ofthe picture (or slice).

In some examples, video decoder 30 may scale the motion vector predictorbefore merging the motion information of the candidate block with block100. For example, with respect to a temporal motion vector predictor, ifthe motion vector predictor refers to a predictive block in a referencepicture that is located in a different temporal location than thepredictive block referred to by block 100 (e.g., the actual motionvector for block 100), video decoder 30 may scale the motion vectorpredictor. For example, video decoder 30 may scale the motion vectorpredictor so that it refers to the same reference picture as thereference picture for block 100. In some examples, video decoder 30 mayscale the motion vector predictor according to a difference in pictureorder count (POC) values. That is, video decoder 30 may scale the motionvector predictor based on a difference between a POC distance betweenthe candidate block and the predictive block referred to by the motionvector predictor and a POC distance between the block 100 and thecurrent reference picture (e.g., referred to by the actual motion vectorfor block 100). After selecting the appropriate motion vector predictor,video decoder 30 may merge the motion information associated with themotion vector predictor with the motion information for block 100.

A similar process may be implemented by video encoder 20 and videodecoder 30 to perform motion vector prediction for a current block ofvideo data. For example, video encoder 20 may initially determine whichmotion vectors from the motion vector predictor candidates are availableto be used as MVPs. Motion information from one or more of the motionvector predictor candidates may be unavailable due to, for example, themotion vector predictor candidate being intra-coded, not yet coded, ornon-existent.

To determine which of the motion vector predictor candidates areavailable, video encoder 20 may analyze each of the motion vectorpredictor candidates in turn according to a predetermined priority basedscheme. For example, for each motion vector predictor candidate, videoencoder 20 may determine whether the motion vector predictor refers tothe same reference picture as the actual motion vector for block 100. Ifthe motion vector predictor refers to the same reference picture, videoencoder 20 may add the motion vector predictor candidate to an MVPcandidate list. If the motion vector predictor does not refer to thesame reference picture, the motion vector predictor may be scaled (e.g.,scaled based on POC distances, as discussed above) before being added tothe MVP candidate list.

With respect to co-located block COL, if the co-located block includesmore than one motion vector predictor (e.g., COL is predicted as aB-frame), video encoder 20 may select one of the temporal motion vectorpredictors according to the current list and the current referencepicture (for block 100). Video encoder 20 may then add the selectedtemporal motion vector predictor to the motion vector predictorcandidate list.

Video encoder 20 may signal that one or more motion vector predictorsare available by setting an enable_temporal_mvp_flag. After building thecandidate list, video encoder 20 may select a motion vector from thecandidates to be used as the motion vector predictor for block 100. Insome examples, video encoder 20 may select the candidate motion vectoraccording to a rate distortion analysis.

Video encoder 20 may signal the selected motion vector predictor usingan MVP index (mvp_flag) that identifies the MVP in the candidate list.For example, video encoder 20 may set mvp_(—)10_flag[x0][y0] to specifythe motion vector predictor index of list 0, where x0, y0 specify thelocation (x0, y0) of the top-left luma sample of the candidate blockrelative to the top-left luma sample of the picture. In another example,video encoder 20 may set mvp_(—)11_flag[x0][y0] to specify the motionvector predictor index of list 1, where x0, y0 specify the location (x0,y0) of the top-left luma sample of the candidate block relative to thetop-left luma sample of the picture. In still another example, videoencoder 20 may set mvp_(—)1c_flag[x0][y0] to specify the motion vectorpredictor index of list c, where x0, y0 specify the location (x0, y0) ofthe top-left luma sample of the candidate block relative to the top-leftluma sample of the picture.

Video encoder 20 may also generate a motion vector difference value(MVD). The MVD may constitute the difference between the selected motionvector predictor and the actual motion vector for block 100. Videoencoder 20 may signal the MVD with the MVP index.

Video decoder 30 may perform similar operations to determine a motionvector for a current block using a motion vector predictor. For example,video decoder 30 may receive an indication in a parameter set (e.g., apicture parameter set (PPS)) indicating that motion vector prediction isenabled for one or more pictures. That is, in an example, video decoder30 may receive an enable_temporal_mvp_flag in a PPS. When a particularpicture references a PPS having an enable_temporal_mvp_flag equal tozero, the reference pictures in the reference picture memory may bemarked as “unused for temporal motion vector prediction.”

If motion vector prediction is implemented, upon receiving block 100,video decoder 30 may construct an MVP candidate list. Video decoder 30may use the same scheme discussed above with respect to video encoder 20to construct the MVP candidate list. In some instances, video decoder 30may perform motion vector scaling similar to that described above withrespect to video encoder 20. For example, if a motion vector predictordoes not refer to the same reference picture as block 100, the motionvector predictor may be scaled (e.g., scaled based on POC distances, asdiscussed above) before being added to the MVP candidate list. Videodecoder 30 may identify the appropriate motion vector predictor forblock 100 using a received MVP index (mvp_flag) that identifies the MVPin the candidate list. Video decoder 30 may then generate the motionvector for block 100 using the MVP and a received MVD.

FIG. 5 generally illustrates merge mode and motion vector prediction ina single view. It should be understood that the motion vector predictorcandidate blocks shown in FIG. 5 are provided for purposes of exampleonly, more, fewer, or different blocks may be used for purposes ofpredicting motion information. According to aspects of this disclosure,as described below, merge mode and motion vector prediction can also beapplied when more than one view is coded (such as in MVC). In suchinstances, motion vector predictors and predictive blocks may be locatedin different views than block 100.

FIG. 6 is a conceptual diagram illustrating generating and scaling amotion vector predictor in multiview coding. For example, according toaspects of this disclosure, a video coder (such as video encoder 20 orvideo decoder 30) may scale a disparity motion vector 120 (mv) from adisparity motion vector predictor candidate block 122 (“candidateblock”) to generate a motion vector predictor 124 (mv′) for currentblock 126. While FIG. 6 is described with respect to video decoder 30,it should be understood that the techniques of this disclosure may becarried out by a variety of other video coders, including otherprocessors, processing units, hardware-based coding units such asencoder/decoders (CODECs), and the like.

In the example of FIG. 6, candidate block 122 spatially neighborscurrent block 126 in view component two (view_id 2). Candidate block 122is inter predicted and includes motion vector 120 that refers (or“points”) to a predictive block in view component zero (view_id 0). Forexample, motion vector 120 has a target picture in view two (view_id 2)and a reference picture in view zero (view_id 0). Current block 126 isalso inter predicted and includes an actual motion vector (not shown)that refers to a predictive block in view component one (view_id 1).That is, for example, the actual motion vector for current block 126 hasa target picture in view two (view_id 2) and a reference block in viewone (view_id 1).

According to aspects of this disclosure, video decoder 30 may generatemotion vector predictor 124 for current block 126 using a scaled versionof motion vector 120. For example, video decoder 30 may scale motionvector 120 based on a difference in view distances between motion vector120 and the actual motion vector for current block 126. That is, videodecoder 30 may scale motion vector 120 based on a difference between thecamera location of a camera used to capture the predictive block (in thereference picture) for candidate block 122 and the predictive block (inthe reference picture) for current block 126. Accordingly, video decoder30 may scale disparity motion vector 120 (e.g., the motion vector beingused for prediction) according to a difference between the viewcomponent referred to by motion vector 120 for candidate block 122 andthe view component referred to by the actual motion vector for currentblock 126.

In an example, video decoder 30 may generate a scaled motion vectorpredictor for a current block according to equation (1) shown below:

$\begin{matrix}{{mv}^{\prime} = {{mv}\left( \frac{{ViewDistance}\left( {mv}^{\prime} \right)}{{ViewDistance}({mv})} \right)}} & (1)\end{matrix}$where ViewDistance(mv) is equal to a difference between a view ID of areference picture of motion vector 120 (e.g., ViewId(RefPic(mv)) and aview ID of a target picture of motion vector 120 (e.g.,ViewId(TargetPic(mv)), and ViewDistance(mv′) is equal to a differencebetween a view ID of a reference picture of motion vector predictor 124(e.g., ViewId(RefPic(mv′)) and a view ID of a target picture of motionvector predictor 124 (e.g., ViewId(TargetPic(mv′)). Accordingly, in thisexample, the reference picture of motion vector predictor 124,RefPic(mv′), belongs to the new target view and the target picture ofmotion vector predictor 124, TargetPic(mv′), belongs to the currentview. Similarly, the reference picture of motion vector 120, RefPic(mv),belongs to the view that the candidate motion vector points to, and thetarget picture of motion vector 120, TargetPic(mv), belongs to thecurrent view. Accordingly, video decoder 30 may generate a scaled motionvector predictor according to equation (2) below:

$\begin{matrix}{{mv}^{\prime} = {{mv}\left( \frac{{{ViewID}({NewTarget})} - {{ViewID}({Current})}}{{{ViewID}({Candidate})} - {{ViewId}({Current})}} \right)}} & (2)\end{matrix}$where mv′ represents the scaled motion vector predictor for the currentblock, my represents the motion vector for the candidate block,ViewID(NewTarget) is the view component referred to by the actual motionvector for the current block, ViewID(Current) is the view component ofthe current block, and ViewID(Candidate) is the view component of thecandidate block.

Applying equation (2) to the example in FIG. 6, mv′ represents thescaled motion vector predictor for current block 126, my representsmotion vector 120, ViewID(NewTarget) is the view component referred toby motion vector 124, ViewID(Current) is the view component of currentblock 126, and ViewID(Candidate) is the view component of candidateblock 122. Accordingly, in the example shown in FIG. 4, motion vectorpredictor 124 is motion vector 120 scaled by a factor of one half (e.g.,

$\left( {{e.g.},\mspace{11mu}{{mv}^{\prime} = {{mv}\left( \frac{1 - 2}{0 - 2} \right)}}} \right).$That is, video decoder 30 may scale both the horizontal displacementcomponent and the vertical displacement component of motion vector 120by a factor of one half to produce motion vector predictor 124 forcurrent block 126.

The motion vector scaling described with respect to FIG. 6 may beperformed for both merging and motion vector prediction. That is, forexample, video decoder 30 may scale motion vector 120 before mergingmotion vector 120 with the motion information for current block 126. Inanother example, video decoder 30 may scale motion vector 120 beforecalculating a motion vector difference value (MVD) according to adifference between motion vector predictor 124 and the actual motionvector for current block 126.

As shown in the example of FIG. 6, candidate block 122 and current block126 may be located in the same view component. However, in otherexamples, as described in greater detail with respect to FIGS. 7 and 8,the candidate block may be located in a different view component thanthe current block.

FIG. 7 is another conceptual diagram illustrating generating and scalinga motion vector predictor. For example, according to aspects of thisdisclosure, a video coder (such as video encoder 20 or video decoder 30)may scale a disparity motion vector 130 (mv) from a disparity motionvector predictor candidate block 132 (x′, y′) to generate motion vectorpredictor 134 (mv′) for a current block 136 (x, y), where candidateblock 132 belongs to a different view component than current block 136.Accordingly, the process shown and described with respect to FIG. 7 maygenerally be referred to as inter-view disparity motion vectorprediction. While FIG. 7 is described with respect to video decoder 30,it should be understood that the techniques of this disclosure may becarried out by a variety of other video coders, including otherprocessors, processing units, hardware-based coding units such asencoder/decoders (CODECs), and the like.

In the example shown in FIG. 7, candidate block 132 is located in viewcomponent one (view_id 1). Candidate block 132 is inter predicted andincludes motion vector 130 (mv) that refers to a predictive block inview component zero (view_id 0). For example, motion vector 130 has atarget picture in view one (view_id 1) and a reference picture in viewzero (view_id 0). Current block 136 is co-located with candidate block132 and located in view component two (view_id 2). As described ingreater detail below, in some examples, current block 136 may include anactual motion vector (not shown) that identifies a block in a firstreference view (view_id 1). That is, for example, the actual motionvector for current block 136 has a target picture in view two (view_id2) and may have a reference block in view one (view_id 1). In otherexamples, current block may include an actual motion vector thatidentifies a block in second reference view (view_id 0). That is, forexample, the actual motion vector for current block 136 has a targetpicture in view two (view_id 2) and a may have a reference block in viewzero (view_id 0). Accordingly, motion vector predictor 134 (mv′) mayrefer to a block in a first reference view (view_id 1). In anotherexample, a second motion vector predictor 138 (mv′) may refer to a blockin a second reference view (view_id 0).

In some examples, the second motion vector predictor 138 may not beavailable for purposes of motion vector prediction. For example, thesecond motion vector predictor 138 may only be generated if a predictiveblock in the second reference view is available for direct inter-viewprediction. The availability of a predictive block in the secondreference view may be specified, for example, in a parameter set (suchas a sequence parameter set (SPS) or picture parameter set (PPS)) orslice header associated with current block 136.

According to the aspects of this disclosure, video decoder may performinter-view disparity motion vector prediction using merge mode or usingmotion vector prediction. With respect to merge mode, video decoder 30may initially select a “target view” for current block 136. In general,the target view includes the predictive block for current block 136. Insome examples, the target view may be the first reference view (shown inFIG. 7 as view_id 1). In other examples, the target view may be thesecond reference view (shown in FIG. 7 as view_id 0). As noted above,however, in some examples, the second reference view may only be used asa target view if a predictive block in the second reference view isavailable to be used for purposes of inter-view prediction.

In some examples, video decoder 30 may select the first reference viewas the target view. In other examples, video decoder 30 may select, whenavailable, the second reference view as the target view. The selectionof the target view may be determined, for example, based on theavailability of a predictive block and/or a predetermined selectionalgorithm. The reference index (ref_idx) of current block 136corresponds to the index of the picture containing the predictive blockof the target view, which is added to the reference picture list ofcurrent block 136.

After selecting the target view, video decoder 30 may locate candidateblock 132. In an example for purposes of illustration, assume theupper-left luma sample of current block 136 is located in a picture (orslice) at coordinates (x, y). Video decoder 30 may determine co-locatedcoordinates in view component one for candidate block 132. In addition,in some examples, video decoder 30 may adjust the coordinates based on adisparity between the view component of current block 136 (viewcomponent two) and the view component of candidate block (view componentone) 132. Accordingly, video decoder 30 may determine the coordinatesfor candidate block 132 as (x′, y′), where (x′, y′)=(x, y)+disparity. Insome examples, the disparity may be included and/or calculated in anSPS, PPS, slice header, CU syntax, and/or PU syntax.

After locating candidate block 132, video decoder 30 may scale motionvector 130 for candidate block 132 based on a difference in viewdistances between motion vector 130 and the actual motion vector forcurrent block 136. That is, video decoder 30 may scale motion vector 130based on a difference in camera location of a camera used to capture thepredictive block for candidate block 132 and the predictive block forcurrent block 136 (e.g., the predictive block in the target view). Thatis, video decoder 30 may scale disparity motion vector 130 (e.g., themotion vector being used for prediction) according to a differencebetween the view component referred to by motion vector 130 forcandidate block 132 and the view component of the target view.

In an example, video decoder 30 may generate a scaled motion vectorpredictor for a current block according to equation (3) shown below:

$\begin{matrix}{{mv}^{\prime} = {{mv}\left( \frac{{{ViewID}({Target})} - {{ViewID}({Current})}}{{{ViewID}({SecondReference})} - {{ViewId}({Reference})}} \right)}} & (3)\end{matrix}$where mv′ represents the scaled motion vector predictor for the currentblock, my represents the motion vector for the candidate block,ViewID(Target) is the view component of the selected target view,ViewID(Current) is the view component of the current block, andViewID(SecondReference) is the view component of the second referenceview (if available), and ViewID(Reference) is the view component of thefirst reference view. In some examples, ViewID(Target) minus theViewID(current) may be referred to as a view distance of motion vectorpredictor 134, while ViewID(SecondReference) minus ViewID(Reference) maybe referred to as the view distance of motion vector 130. That is, theview distance of motion vector predictor 134 is the difference betweenthe target picture (view_id 1) and the reference picture (view_id 2) ofmotion vector predictor 134, while the view distance of motion vector130 is the difference between the target picture (view_id 0) and thereference picture (view_id 1) of motion vector 130.

Applying equation (3) to the example in FIG. 7, mv′ represents eitherthe scaled motion vector predictor 134 or the scaled motion vectorpredictor 138, depending on which view component is selected for thetarget view. For example, if the first reference view (view_id 1) isselected as the target view, mv′ represents the scaled motion vectorpredictor 134, my represents motion vector 130, ViewID(Target) is theview component referred to by motion vector predictor 134,ViewID(Current) is the view component of current block 136,ViewID(SecondReference) is the view component of the second referenceview (view_id 0), and ViewID(Reference) is the view component of thefirst reference view (view_id 1). Accordingly, in the example shown inFIG. 7, motion vector predictor 134 is motion vector 130 scaled by afactor of one (e.g.,

$\left( {{e.g.},{{mv}^{\prime} = {{mv}\left( \frac{1 - 2}{0 - 1} \right)}}} \right).$That is, the horizontal displacement component and the verticaldisplacement component of motion vector 130 may be the same as thehorizontal displacement component and the vertical displacementcomponent of motion vector predictor 134.

Alternatively, if the second reference view (view_id 0) is selected forthe target view, mv′ represents the scaled motion vector predictor 138,my represents motion vector 130, ViewID(Target) is the view componentreferred to by motion vector predictor 138, ViewID(Current) is the viewcomponent of current block 136, ViewID(SecondReference) is the viewcomponent of the second reference view (view_id 0), andViewID(Reference) is the view component of the first reference view(view_id 1). Accordingly, in the example shown in FIG. 7, motion vectorpredictor 138 is motion vector 130 scaled by a factor of two (e.g.,

$\left( {{e.g.},{{mv}^{\prime} = {{mv}\left( \frac{0 - 2}{0 - 1} \right)}}} \right).$That is, video decoder 30 may scale both the horizontal displacementcomponent and the vertical displacement component of motion vector 130by a factor of two to produce motion vector predictor 138 for currentblock 136.

According to aspects of this disclosure, video decoder 30 may performsimilar steps when performing motion vector prediction (e.g., generatingan MVP). For example, video decoder 30 may select a target view, whichmay be the first reference view (view_id 1) or the second reference view(view_id 0). However, if a reference picture of the view componentcontaining a predictive block for current block is not available forpurposes of inter-view prediction, the corresponding predictor may notbe used. Accordingly, the selection of the target view may bedetermined, for example, based on the availability of a predictive blockand/or a predetermined selection algorithm.

If a predictive block for current block 136 is not available to be usedfor direct inter-view prediction in either the first reference view(view_id 1) or the second reference view (view_id 0), video decoder 30may not perform motion vector prediction. If at least on predictiveblock is available, video decoder 30 may select the reference view thatincludes the predictive block associated with the actual motion vectorfor current block 136.

After selecting a target view, video decoder 30 may then repeat thesteps described above with respect to merge mode. For example, videodecoder 30 may locate candidate block 132. That is, video decoder 30 maydetermine co-located coordinates in view component one for candidateblock 132. In addition, in some examples, video decoder 30 may adjustthe coordinates based on a disparity between the view component ofcurrent block 136 (view component two) and the view component ofcandidate block (view component one) 132.

In addition, after locating candidate block 132, video decoder 30 mayscale motion vector 130 for candidate block 132 based on a difference incamera location of a camera used to capture the predictive block forcandidate block 132 and the predictive block for current block 136(e.g., the predictive block in the target view). That is, video decoder30 may scale disparity motion vector 130 (e.g., the motion vector beingused for prediction) according to a difference between the viewcomponent referred to by motion vector 130 for candidate block 132 andthe view component of the target view.

In some examples, video decoder 30 may perform motion vector predictorscaling using equation (2) above. In other examples, as described withrespect to FIG. 8 below, motion vector predictor scaling may be expandedto other views.

Video decoder 30 may add candidate block 132 to a candidate list whenperforming merge mode and/or motion vector prediction (described, forexample, with respect to FIG. 5 above). According to aspects of thisdisclosure, candidate block may be added to the motion vector predictorcandidate list (e.g., for either merge mode or motion vector predictionwith an MVP) in a variety of ways. For example, video decoder 30 mayconstruct the candidate list by locating merge mode candidates accordingto the following scheme:

1. A₁, if availableFlagA₁ is equal to 1

2. V, if availableFlagV is equal to 1

3. B₁, if availableFlagB₁ is equal to 1

4. B₀, if availableFlagB₀ is equal to 1

5. A₀, if availableFlagA₀ is equal to 1

6. B₂, if availableFlagB₂ is equal to 1

7. Col, if availableFlagCol is equal to 1

where V represents candidate block 132. In other examples, candidateblock 132 may be located and added to the candidate list in any otherposition of the candidate list.

FIG. 8 is another conceptual diagram illustrating generating and scalinga motion vector predictor, according to aspects of this disclosure. Forexample, according to aspects of this disclosure, a video coder (such asvideo encoder 20 or video decoder 30) may scale a disparity motionvector 140 (mv) from a disparity motion vector predictor candidate block142 to generate motion vector predictor 144 (mv′) for a current block146, where candidate block 142 belongs to a different view componentthan current block 146. While FIG. 8 is described with respect to videodecoder 30, it should be understood that the techniques of thisdisclosure may be carried out by a variety of other video coders,including other processors, processing units, hardware-based codingunits such as encoder/decoders (CODECs), and the like.

The example shown in FIG. 8 expands the motion vector prediction shownand described with respect to FIG. 7 to an environment that includesmore than three views. For example, as shown in FIG. 8, candidate block142 is located in view component two (view_id 2). Candidate block 142 isinter predicted and includes motion vector 140 (mv) that refers to apredictive block in view component one (view_id 1). For example, motionvector 140 has a target picture in view two (view_id 2) and a referencepicture in view one (view_id 1). Current block 146 is co-located withcandidate block 142 and located in view component three (view_id 3).

According to aspects of this disclosure, video decoder 30 may select atarget view for current block 146 as view component zero (view_id 0).For example, the target view generally includes the predictive block forcurrent block. If the picture containing the predictive block is aninter-view reference picture, and the predictive block for current block146 is located in a third reference view (view_id 0), video decoder 30may select the third reference view as the target view.

After selecting the target view, video decoder 30 may locate candidateblock 142. For example, assuming the upper-left luma sample of currentblock 146 is located in a picture (or slice) at coordinates (x,y) inview component three, video decoder 30 may determine co-locatedcoordinates in view component two for candidate block 142. In addition,as noted above, video decoder 30 may adjust the coordinates based on adisparity between the view component of current block 146 (viewcomponent three) and the view component of candidate block (viewcomponent two) 142.

After locating candidate block 142, video decoder 30 may scale motionvector 140 for candidate block 142 based on a difference in viewdistances between motion vector 140 and the actual motion vector forcurrent block 146. That is, video decoder 30 may scale motion vector 130based on a difference in camera location of a camera used to capture thepredictive block for candidate block 142 and the predictive block forcurrent block 146 (e.g., the predictive block in the target view). Thatis, video decoder 30 may scale disparity motion vector 140 (e.g., themotion vector being used for prediction) according to a differencebetween the view component referred to by motion vector 140 forcandidate block 142 and the view component of the target view (view_id0).

In an example, video decoder 30 may generate a scaled motion vectorpredictor for a current block according to equation (4) shown below:

$\begin{matrix}{{mv}^{\prime} = {{mv}\left( \frac{{{ViewID}({Third})} - {{ViewID}({Current})}}{{{ViewID}({SecondReference})} - {{ViewId}({Reference})}} \right)}} & (4)\end{matrix}$where mv′ represents the scaled motion vector predictor for the currentblock, my represents the motion vector for the candidate block,ViewID(Third) is the view component of the third reference view,ViewID(Current) is the view component of the current block, andViewID(SecondReference) is the view component of the second referenceview (if available), and ViewID(Reference) is the view component of thefirst reference view. In some examples, ViewID(Third) minus theViewID(current) may be referred to as a view distance of motion vectorpredictor 144, while ViewID(SecondReference) minus ViewID(Reference) maybe referred to as the view distance of motion vector 140. That is, theview distance of motion vector predictor 144 is the difference betweenthe target picture (view_id 0) and the reference picture (view_id 3) ofmotion vector predictor 144, while the view distance of motion vector140 is the difference between the target picture (view_id 1) and thereference picture (view_id 2) of motion vector 140.

Applying equation (3) to the example in FIG. 8, mv′ represents thescaled motion vector predictor 144. For example, ViewID(Third) is thethird reference view (view_id 0), mv′ represents the scaled motionvector predictor 144, my represents motion vector 140, ViewID(Current)is the view component of current block 146, ViewID(SecondReference) isthe view component of the second reference view (view_id 1), andViewID(Reference) is the view component of the first reference view(view_id 2). Accordingly, in the example shown in FIG. 8, motion vectorpredictor 144 is motion vector 140 scaled by a factor of three (e.g.,

$\left( {{e.g.},\mspace{11mu}{{mv}^{\prime} = {{mv}\left( \frac{0 - 3}{1 - 2} \right)}}} \right).$That is, video decoder 30 may scale the horizontal displacementcomponent and the vertical displacement component of motion vector 140by three to form motion vector predictor 144.

While FIGS. 7-8 provide examples for inter-view disparity motion vectorprediction, it should be understood that such examples are providedmerely for purposes of illustration. That is, the techniques fordisparity motion vector prediction may be applied to more or fewer viewsthan those shown. Additionally or alternatively, the techniques fordisparity motion vector prediction may be applied in circumstances inwhich views have different view identifiers.

FIG. 9 is a flow diagram illustrating an example method of codingprediction information for a block of video data. The example shown inFIG. 9 is generally described as being performed by a video coder. Itshould be understood that, in some examples, the method of FIG. 9 may becarried out by video encoder 20 (FIGS. 1 and 2) or video decoder 30(FIGS. 1 and 3), described above. In other examples, the method of FIG.9 may be performed by a variety of other processors, processing units,hardware-based coding units such as encoder/decoders (CODECs), and thelike.

According to the example method shown in FIG. 9, a video coder mayidentify a first block of video data in a first view, where the firstblock of video data is associated with a first disparity motion vector(160). For example, the motion vector for the first block of video datamay be a disparity motion vector that identifies a reference block inanother view component. The video coder may then determine whether asecond motion vector associated with a second block of video data is adisparity motion vector (162).

If the second motion vector is not a disparity motion vector (the NObranch of step 162), the video coder may identify a different motionvector predictor candidate (164). That is, according to some aspects ofthis disclosure, the ability to use a disparity motion vector (e.g., thefirst motion vector) to predict a temporal motion vector (e.g., thesecond motion vector, when the second motion vector is a temporal motionvector) may be disabled. In such instances, the video coder may identifythe first motion vector as being unavailable to be used for purposes ofmotion vector prediction.

If the second motion vector is a disparity motion vector (the YES branchof step 162), the video coder may scale the first motion vector togenerate a motion vector predictor for the second motion vector (166).For example, according to aspects of this disclosure, the video codermay scale the first motion vector to generate the disparity motionvector predictor based on differences in view distances associated withthe first disparity motion vector and the second motion vector. That is,in some examples, the video coder may scale the motion vector predictorfor the second block based on camera locations. For example, the videocoder may scale the second motion vector according to a difference inview identifiers as shown and described with respect to FIGS. 6-8.

The video coder may then code prediction data for the second block usingthe scaled motion vector predictor (168). For example, the video codermay code the prediction data for the second block using merge mode orusing motion vector prediction. For merge mode, the video coder maydirectly code the prediction data for the second block using the scaledsecond motion vector predictor. For motion vector prediction, the videocoder may code the prediction data for the second block by generating anMVD. The MVD may include the difference between the first motion vectorand the scaled second motion vector.

It should also be understood that the steps shown and described withrespect to FIG. 9 are provided as merely one example. That is, the stepsof the method of FIG. 9 need not necessarily be performed in the ordershown in FIG. 9, and fewer, additional, or alternative steps may beperformed.

FIG. 10 is a conceptual diagram illustrating generating a motion vectorpredictor from a block in a different view than a current block. Forexample, according to aspects of this disclosure, a video coder (such asvideo encoder 20 or video decoder 30) may use a temporal motion vector180 (mv) from a temporal motion vector predictor candidate block 182 togenerate motion vector predictor 184 (mv′) for a current block 186,where candidate block 182 belongs to a different view component thancurrent block 186. While FIG. 10 is described with respect to videodecoder 30, it should be understood that the techniques of thisdisclosure may be carried out by a variety of other video coders,including other processors, processing units, hardware-based codingunits such as encoder/decoders (CODECs), and the like.

As shown in FIG. 10, current block 186 is located in view component one(view_id 1). Candidate block 182 is located in view component zero(view_id 0). Candidate block 182 is temporally predicted and includesmotion vector 180 (mv) that refers to a predictive block in a differenttemporal location within the same view component. That is, in theexample shown in FIG. 10, motion vector 180 identifies a predictiveblock in a picture having a reference index equal to variable i(ref_idx=i).

Assume the upper-left luma sample of current block 186 is located in apicture (or slice) at coordinates (x,y). Video decoder 30 may locatecandidate block 182 by determining co-located coordinates in viewcomponent zero for candidate block 182. In some examples, video decoder30 may adjust the coordinates of candidate block 182 based on adisparity between the view component of current block 186 (view_id 1)and the view component of candidate block 182 (view_id 0). Accordingly,video decoder 30 may determine the coordinates for candidate block 182as (x′, y′), where (x′, y′)=(x, y)+disparity. In some examples, thedisparity may be included and/or calculated in an SPS, PPS, sliceheader, CU syntax, and/or PU syntax.

According to aspects of this disclosure, video decoder 30 may thenre-map the reference index of motion vector 180 being used for purposesof prediction. In general, as noted above, data for a motion vectorincludes a reference picture list, an index into the reference picturelist (referred to as ref_idx), a horizontal component, and a verticalcomponent. In HEVC, there may be two normal reference picture lists,(e.g., list 0 and list 1) and a combined reference picture list (e.g.,list c). Without loss of generality, assume the current referencepicture list is list t (which may correspond to any of list 0, list 1,or list c). According to the example shown in FIG. 10, motion vector 180for candidate block 182 may identify a predictive block in a picturelocated in view component zero (view_id 0) having a POC value of two anda ref_idx equal to i. According to aspects of this disclosure, videodecoder 30 may identify a co-located predictive block for current block186 in the same time instance as current block 186. That is, thepredictive block for candidate block 182 and the predictive block forcurrent block 186 have the same temporal location, but are located inpictures of two different views.

In an example, if the identified predictive block for current block 186corresponds to the j-th reference picture in the reference picture listt for the current picture, video decoder 30 may predict the referenceindex (ref_idx) for current block 186 as j, and video decoder 30 may setmotion vector predictor 184 to the same value as motion vector 180.Accordingly, video decoder 30 effectively re-maps the reference indexfor current block 186 from ref_idx i to ref_idx j. That is, videodecoder 30 determines that motion vector predictor 184 for current block186 has the same reference picture list, horizontal component, andvertical component as candidate block 182, however, the motion vectorpredictor 184 refers to the j-th reference picture in the referencepicture list, rather than the i-th reference picture in the referencepicture list.

According to aspects of this disclosure, in some examples, video decodermay also scale motion vector predictor 184. For example, if the picturecontaining the identified predictive block for current block 186 is notincluded in the reference picture list t, video decoder 30 may identifya second picture that is closest in the reference picture list t. Insome examples, if two pictures have identical distances to the picturecontaining the identified predictive block for current block 186, videodecoder 30 may select the picture that is closer to the picturecontaining current block 186 as the second picture. Assume for purposesof explanation that the identified picture has a reference index of k.In this example, video decoder 30 may then predict the reference indexof motion vector predictor 184 as k, and video decoder 30 may scalemotion vector predictor 184 based on a difference in picture order count(POC). That is, video decoder 30 may scale motion vector predictor 184based on a difference between the distance between current block 186 andthe picture at reference index j, and current block 186 and the pictureat reference index k.

According to some examples, video decoder 30 may perform the sameprocess when performing motion vector prediction. However, afterdetermining motion vector predictor 184, video decoder 30 may generatethe motion vector for current block 186 using an MVD. Motion vectorprediction may use the same process. In another example, with respect tomotion vector prediction, if a predictive block for current block 186cannot be located (identified as being located at reference index jabove), video decoder 30 may not perform merge mode or motion vectorprediction for current block 186. That is, rather than scaling motionvector predictor 184, video decoder 30 may consider motion vectorpredictor 184 unavailable.

Video decoder 30 may add candidate block 182 to a candidate list forperforming merge mode and/or motion vector prediction (described, forexample, with respect to FIG. 5 above). According to aspects of thisdisclosure, candidate block 182 may be added to the motion vectorpredictor candidate list (e.g., for either merge mode or motion vectorprediction with an MVP) in a variety of ways. For example, video decoder30 may construct the candidate list by locating candidates according tothe following scheme:

1. A₁, if availableFlagA₁ is equal to 1

2. V, if availableFlagV is equal to 1

3. B₁, if availableFlagB₁ is equal to 1

4. B₀, if availableFlagB₀ is equal to 1

5. A₀, if availableFlagA₀ is equal to 1

6. B₂, if availableFlagB₂ is equal to 1

7. Col, if availableFlagCol is equal to 1

where V represents candidate block 182. In other examples, candidateblock 132 may be located and added to the candidate list in any otherposition of the candidate list.

FIG. 11 is a flow diagram illustrating an example method of generating amotion vector predictor. The example shown in FIG. 11 is generallydescribed as being performed by a video coder. It should be understoodthat, in some examples, the method of FIG. 11 may be carried out byvideo encoder 20 (FIGS. 1 and 2) or video decoder 30 (FIGS. 1 and 3),described above. In other examples, the method of FIG. 11 may beperformed by a variety of other processors, processing units,hardware-based coding units such as encoder/decoders (CODECs), and thelike.

According to the example shown in FIG. 11, the video coder may identifya first block of video data in a first temporal location of a firstview, where the first block is associated with a first temporal motionvector (202). According to aspects of this disclosure, when a secondmotion vector associated with a second block of video data is a temporalmotion vector and the second block is from a second, different view thanthe first block (the YES branch of step 204), the video coder maydetermine a motion vector predictor based on the first motion vector(206). That is, for example, the video coder may determine a motionvector predictor for predicting the second motion vector from the firstmotion vector. The video coder may also code prediction data for thesecond block using the motion vector predictor (208). For example, thevideo coder may use the motion vector predictor in a merge mode or togenerate an MVD value.

If the second motion vector is not a temporal motion vector and/or thesecond block of video data is not from a different view than the firstblock of video data (the NO branch of step 204), the video coder maydetermine whether the second motion vector is a disparity motion vector(210). According to aspects of this disclosure, if the second motionvector is not a disparity motion vector (the NO branch of step 210), thevideo coder may identify a different motion vector predictor candidate(212). That is, the video coder may, in some examples, not use the firstmotion vector to predict the second motion vector.

If the second motion vector is a disparity motion vector (the YES branchof step 210), the video coder may determine whether disparity motionvector prediction is disabled (214). That is, according to some aspectsof this disclosure, the ability to use a temporal motion vector (e.g.,the first motion vector) to predict a disparity motion vector (e.g., thesecond motion vector, when the second motion vector is a disparitymotion vector) may be disabled. In such instances, the video coder mayidentify a different motion vector predictor candidate (212) (the NObranch of step 214).

If the video coder determines that disparity motion vector prediction isenabled (e.g., or the ability to enable/disable such a function is notpresent) the video coder may determine a motion vector predictor for thesecond motion vector based on the first motion vector (206) (the YESbranch of step 214). In addition, the video coder may also codeprediction data for the second block using the motion vector predictor(208). For example, the video coder may use the motion vector predictorin a merge mode or to generate an MVD value.

It should also be understood that the steps shown and described withrespect to FIG. 11 are provided as merely one example. That is, thesteps of the method of FIG. 11 need not necessarily be performed in theorder shown in FIG. 11, and fewer, additional, or alternative steps maybe performed.

It should be understood that, depending on the example, certain acts orevents of any of the methods described herein can be performed in adifferent sequence, may be added, merged, or left out all together(e.g., not all described acts or events are necessary for the practiceof the method). Moreover, in certain examples, acts or events may beperformed concurrently, e.g., through multi-threaded processing,interrupt processing, or multiple processors, rather than sequentially.In addition, while certain aspects of this disclosure are described asbeing performed by a single module or unit for purposes of clarity, itshould be understood that the techniques of this disclosure may beperformed by a combination of units or modules associated with a videocoder.

In one or more examples, the functions described may be implemented inhardware, software, firmware, or any combination thereof. If implementedin software, the functions may be stored on or transmitted over as oneor more instructions or code on a computer-readable medium and executedby a hardware-based processing unit. Computer-readable media may includecomputer-readable storage media, which corresponds to a tangible mediumsuch as data storage media, or communication media including any mediumthat facilitates transfer of a computer program from one place toanother, e.g., according to a communication protocol.

In this manner, computer-readable media generally may correspond to (1)tangible computer-readable storage media which is non-transitory or (2)a communication medium such as a signal or carrier wave. Data storagemedia may be any available media that can be accessed by one or morecomputers or one or more processors to retrieve instructions, codeand/or data structures for implementation of the techniques described inthis disclosure. A computer program product may include acomputer-readable medium.

By way of example, and not limitation, such computer-readable storagemedia can comprise RAM, ROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage, or other magnetic storage devices, flashmemory, or any other medium that can be used to store desired programcode in the form of instructions or data structures and that can beaccessed by a computer. Also, any connection is properly termed acomputer-readable medium. For example, if instructions are transmittedfrom a website, server, or other remote source using a coaxial cable,fiber optic cable, twisted pair, digital subscriber line (DSL), orwireless technologies such as infrared, radio, and microwave, then thecoaxial cable, fiber optic cable, twisted pair, DSL, or wirelesstechnologies such as infrared, radio, and microwave are included in thedefinition of medium.

It should be understood, however, that computer-readable storage mediaand data storage media do not include connections, carrier waves,signals, or other transient media, but are instead directed tonon-transient, tangible storage media. Disk and disc, as used herein,includes compact disc (CD), laser disc, optical disc, digital versatiledisc (DVD), floppy disk and blu-ray disc where disks usually reproducedata magnetically, while discs reproduce data optically with lasers.Combinations of the above should also be included within the scope ofcomputer-readable media.

Instructions may be executed by one or more processors, such as one ormore digital signal processors (DSPs), general purpose microprocessors,application specific integrated circuits (ASICs), field programmablelogic arrays (FPGAs), or other equivalent integrated or discrete logiccircuitry. Accordingly, the term “processor,” as used herein may referto any of the foregoing structure or any other structure suitable forimplementation of the techniques described herein. In addition, in someaspects, the functionality described herein may be provided withindedicated hardware and/or software modules configured for encoding anddecoding, or incorporated in a combined codec. Also, the techniquescould be fully implemented in one or more circuits or logic elements.

The techniques of this disclosure may be implemented in a wide varietyof devices or apparatuses, including a wireless handset, an integratedcircuit (IC) or a set of ICs (e.g., a chip set). Various components,modules, or units are described in this disclosure to emphasizefunctional aspects of devices configured to perform the disclosedtechniques, but do not necessarily require realization by differenthardware units. Rather, as described above, various units may becombined in a codec hardware unit or provided by a collection ofinteroperative hardware units, including one or more processors asdescribed above, in conjunction with suitable software and/or firmware.

Various aspects of the disclosure have been described. These and otheraspects are within the scope of the following claims.

What is claimed is:
 1. A method of coding video data, the methodcomprising: identifying a first block of video data in a first temporallocation from a first view, wherein the first block of video data isassociated with a first temporal motion vector; determining, when asecond motion vector associated with a second block of video data is atemporal motion vector and the second block is from a second view thatis different than the first view, a motion vector predictor for thesecond motion vector based on the first temporal motion vector, whereindetermining the motion vector predictor comprises determining the motionvector predictor without scaling the motion vector predictor when apicture order count (POC) value of a reference picture of the secondmotion vector is the same as a POC value of a reference picture of thefirst motion vector; constructing a motion vector predictor candidatelist that includes data identifying the motion vector predictor; andcoding prediction data for the second block using the motion vectorpredictor from the motion vector predictor candidate list.
 2. The methodof claim 1, wherein, when the second motion vector is a disparity motionvector, disabling an ability to determine the motion vector predictorfrom the first motion vector.
 3. The method of claim 1, furthercomprising, when the POC value of the reference picture of the secondmotion vector is different than the POC value of the reference pictureof the first motion vector, scaling the first motion vector based on adifference in temporal distance between the first temporal motion vectorand the second temporal motion vector before determining the motionvector predictor.
 4. The method of claim 3, wherein the temporaldistance comprises a POC difference between a POC value of a referencepicture and a POC value of target picture of a motion vector.
 5. Themethod of claim 1, further comprising, when a reference picture of thesecond motion vector is the same as a POC of a reference picture of thefirst motion vector, disabling an ability to determine the motion vectorpredictor based on the first temporal motion vector.
 6. The method ofclaim 1, wherein coding the prediction data comprises coding a motionvector difference value using the motion vector predictor.
 7. The methodof claim 1, further comprising locating the first block by identifying alocation in the first picture that is co-located with a location of thesecond block and that is adjusted according to a disparity between thefirst block of the first view and the second block of the second view.8. The method of claim 1, wherein constructing the motion vectorpredictor candidate list comprises constructing the motion vectorpredictor candidate list to include data identifying a picture includingthe second block of video data for the motion vector predictor and dataidentifying one or more other blocks of video data for one or more othermotion vector predictors.
 9. The method of claim 1, wherein coding theprediction data comprises decoding the prediction data and whereindecoding the prediction data comprises identifying the picture in themotion vector predictor candidate list using an index to the motionvector predictor candidate list.
 10. The method of claim 1, whereincoding the prediction data comprises encoding the prediction data. 11.The method of claim 1, wherein coding the prediction data comprisesdecoding the prediction data.
 12. An apparatus for coding video datacomprising: a memory configured to store video data that includes afirst block of video data and a second block of video data and one ormore processors configured to: identify the first block of video data ina first temporal location from a first view, wherein the first block ofvideo data is associated with a first temporal motion vector; determine,when a second motion vector associated with the second block of videodata is a temporal motion vector and the second block is from a secondview that is different than the first view, a motion vector predictorfor the second motion vector based on the first temporal motion vector,wherein to determine the motion vector predictor, the one or moreprocessors are configured to determine the motion vector predictorwithout scaling the motion vector predictor when a picture order count(POC) value of a reference picture of the second motion vector is thesame as a POC value of a reference picture of the first motion vector;construct a motion vector predictor candidate list that includes dataidentifying the motion vector predictor; and code prediction data forthe second block using the motion vector predictor from the motionvector predictor candidate list.
 13. The apparatus of claim 12, whereinthe one or more processors are further configured to, when the secondmotion vector is a disparity motion vector, disable an ability todetermine the motion vector predictor from the first motion vector. 14.The apparatus of claim 12, wherein the one or more processors arefurther configured to, when the POC value of the reference picture ofthe second motion vector is different than the POC value of thereference picture of the first motion vector, scale the first motionvector based on a difference in temporal distance between the firsttemporal motion vector and the second temporal motion vector beforedetermining the motion vector predictor.
 15. The apparatus of claim 14,wherein the temporal distance comprises a POC difference between a POCvalue of a reference picture and a POC value of a target picture of amotion vector.
 16. The apparatus of claim 12, wherein the one or moreprocessors are further configured to, when a reference picture of thesecond motion vector is the same as a POC of a reference picture of thefirst motion vector, disable an ability to determine the motion vectorpredictor based on the first temporal motion vector.
 17. The apparatusof claim 12, wherein the one or more processors are configured to codethe prediction data by coding a motion vector difference value using themotion vector predictor.
 18. The apparatus of claim 12, wherein the oneor more processors are further configured to locate the first block byidentifying a location in the first picture that is co-located with alocation of the second block and that is adjusted according to adisparity between the first block of the first view and the second blockof the second view.
 19. The apparatus of claim 12, wherein to constructthe motion vector predictor candidate list, the one or more processorsare configured to construct the motion vector predictor candidate listto contain data identifying a picture including the second block ofvideo data for the motion vector predictor and data identifying one ormore other blocks of video data for one or more other motion vectorpredictors.
 20. The apparatus of claim 12, wherein to code theprediction data, the one or more processors are configured to decode theprediction data, and wherein to decode the prediction data the one ormore processors are configured to identify the picture in the motionvector predictor candidate list using an index to the motion vectorpredictor candidate list.
 21. The apparatus of claim 12, furthercomprising a camera configured to capture the first block and the secondblock, and wherein to code the prediction data, the one or moreprocessors are configured to encode the second block.
 22. The apparatusof claim 12, wherein to code the prediction data, the one or moreprocessors are configured to decode the second block, the apparatusfurther comprising a display configured to display the first block andthe second block.
 23. An apparatus for coding video data comprising:means for identifying a first block of video data in a first temporallocation from a first view, wherein the first block of video data isassociated with a first temporal motion vector; means for determining,when a second motion vector associated with a second block of video datais a temporal motion vector and the second block is from a second viewthat is different than the first view, a motion vector predictor for thesecond motion vector based on the first temporal motion vector, whereinthe means for determining the motion vector predictor comprises meansfor determining the motion vector predictor without scaling the motionvector predictor when a picture order count (POC) value of a referencepicture of the second motion vector is the same as a POC value of areference picture of the first motion vector; means for constructing amotion vector predictor candidate list that includes data identifyingthe motion vector predictor; and means for coding prediction data forthe second block using the motion vector predictor from the motionvector predictor candidate list.
 24. The apparatus of claim 23, furthercomprising means for disabling, when the second motion vector is adisparity motion vector, an ability to determine the motion vectorpredictor from the first motion vector.
 25. The apparatus of claim 23,further comprising, when the POC value of the reference picture of thesecond motion vector is different than the POC value of the referencepicture of the first motion vector, means for scaling the first motionvector based on a difference in temporal distance between the firsttemporal motion vector and the second temporal motion vector beforedetermining the motion vector predictor.
 26. The apparatus of claim 25,wherein the temporal distance comprises a POC difference between a POCvalue of a reference picture and a POC value of a target picture of amotion vector.
 27. The apparatus of claim 23, further comprising, when areference picture of the second motion vector is the same as a POC of areference picture of the first motion vector, means for disabling anability to determine the motion vector predictor based on the firsttemporal motion vector.
 28. The apparatus of claim 23, wherein the meansfor coding the prediction data comprises means for coding a motionvector difference value using the motion vector predictor.
 29. Theapparatus of claim 23, further comprising means for locating the firstblock by identifying a location in the first picture that is co-locatedwith a location of the second block and that is adjusted according to adisparity between the first block of the first view and the second blockof the second view.
 30. The apparatus of claim 23, wherein the means forconstructing the motion vector predictor candidate list comprises meansfor constructing the motion vector predictor candidate list to includedata identifying a picture including the second block of video data forthe motion vector predictor and data identifying one or more otherblocks of video data for one or more other motion vector predictors. 31.The apparatus of claim 23, wherein the means for coding the predictiondata comprises means for decoding the prediction data, and wherein themeans for decoding the prediction data comprises means for identifyingthe picture in the motion vector predictor candidate list using an indexto the motion vector predictor candidate list.
 32. The apparatus ofclaim 23, wherein the means for coding the prediction data comprisesmeans for encoding the prediction data.
 33. The apparatus of claim 23,wherein the means for coding the prediction data comprises means fordecoding the prediction data.
 34. A non-transitory computer-readablestorage medium having stored thereon instructions that, upon execution,cause one or more processors to: identify a first block of video data ina first temporal location from a first view, wherein the first block ofvideo data is associated with a first temporal motion vector; determine,when a second motion vector associated with a second block of video datais a temporal motion vector and the second block is from a second viewthat is different than the first view, a motion vector predictor for thesecond motion vector based on the first temporal motion vector, whereinto determine the motion vector predictor, the instructions cause the oneor more processors to determine the motion vector predictor withoutscaling the motion vector predictor when a picture order count (POC)value of a reference picture of the second motion vector is the same asa POC value of a reference picture of the first motion vector; constructa motion vector predictor candidate list that includes data identifyingthe motion vector predictor; and code prediction data for the secondblock using the motion vector predictor from the motion vector predictorcandidate list.
 35. The computer-readable storage medium of claim 34,further comprising, when the second motion vector is a disparity motionvector, instructions that cause the one or more processors to disable anability to determine the motion vector predictor from the first motionvector.
 36. The non-transitory computer-readable storage medium of claim34, further comprising, when the POC value of the reference picture ofthe second motion vector is different than the POC value of thereference picture of the first motion vector, instructions that causethe one or more processors to scale the first motion vector based on adifference in temporal distance between the first temporal motion vectorand the second temporal motion vector before determining the motionvector predictor.
 37. The non-transitory computer-readable storagemedium of claim 36, wherein the temporal distance comprises a POCdifference between a reference picture and a target picture of a motionvector.
 38. The non-transitory computer-readable storage medium of claim34, further comprising, when a reference picture of the second motionvector is the same as a POC of a reference picture of the first motionvector, instructions that cause the one or more processors to disable anability to determine the motion vector predictor based on the firsttemporal motion vector.
 39. The non-transitory computer-readable storagemedium of claim 34, wherein the instructions that cause the one or moreprocessors to code the prediction data comprise instructions that causethe one or more processors to code a motion vector difference valueusing the motion vector predictor.
 40. The non-transitorycomputer-readable storage medium of claim 34, further comprisinginstructions that cause the one or more processors to locate the firstblock by identifying a location in the first picture that is co-locatedwith a location of the second block and that is adjusted according to adisparity between the first block of the first view and the second blockof the second view.
 41. The non-transitory computer-readable storagemedium of claim 34, wherein the instructions that cause the one or moreprocessors to construct a candidate list comprise instructions thatcause the one or more processors to construct the motion vectorpredictor candidate list to include data identifying a picture includingthe second block of video data for the motion vector predictor and dataidentifying one or more other blocks of video data for one or more othermotion vector predictors.
 42. The non-transitory computer-readablestorage medium of claim 41, wherein, to code the prediction data, theinstructions cause the one or more processors to decode the predictiondata, and to decode the prediction data the instructions cause the oneor more processors to identify the picture in the motion vectorpredictor candidate list using an index to the motion vector predictorcandidate list.
 43. The non-transitory computer-readable storage mediumof claim 34, wherein instructions that cause the one or more processorsto code the prediction data comprise instructions that cause the one ormore processors to encode the prediction data.
 44. The non-transitorycomputer-readable storage medium of claim 34, wherein instructions thatcause the one or more processors to code the prediction data compriseinstructions that cause the one or more processors to decode theprediction data.